The Linux Command Line
find Size units: w
2-byte words
ls -l /boot/grub>> ls-output.txt
Append redirected output of the ls -l /boot/grub command to ls-output.txt.
kill -18 or kill -cont
Continue. This will restore a program after a STOP signal.
vmstat #
Continuous display of vmstat with a time delay of # sec.
Vim (Text Deletion Commands) - d0
Deletes from the current cursor location to the beginning of the line.
Vim (Text Deletion Commands) - 3x
Deletes the current character and the next two characters.
Vim (Text Deletion Commands) - x
Deletes the current character.
Vim (Text Deletion Commands) - 5dd
Deletes the current line and the next four lines.
apropos
Display a list of appropriate commands.
locate bin/zip
Display a list of files ending in bin/zip
TAB-TAB
Display a list of possible completions.
whatis
Display a very brief description of a command.
apropos searchterm
Display appropriate commands relevant to searchterm.
Less: h
Display help screen.
rm -v or rm --verbose
Display informative messages as the deletion is performed.
mv -v or mv --verbose
Display informative messages as the move is performed.
ls -ltr
Display long results with most recent files last.
Environment Variable: LANG
Defines the character set and collation order of your language.
rm -r file1 dir1
Delete file1 and dir1 (and its contents)
rm -rf file1 dir1
Delete file1 and dir1 (and its contents). If either file1 or dir1 does not exist, rm will continue without a prompt.
rm file1
Delete file1.
Package management system: Low level tools
Handle tasks such as installing and removing package files (dpkg)
Additions to .bashrc: export HISTSIZE=1000
Increases the size of the command history from the default of 500 lines to 1000 lines.
type
Indicate how a command name is interpreted.
Vim - ~
Indicate that no text exists on that line.
Metacharacters: Multiple ranges: [A-Za-z0-9]
Indicates the ranges A-Z, a-z, and 0-9.
Vim (Moving the Cursor Around) - CTRL-b or PAGE UP
Moves cursor up one page.
How do you access the virtual terminal/console?
Press CTRL-ALT-F1 through CTRL-ALT-F6.
Domain name
Typically a web address linked to an IP address.
Login Shell Session Startup Files: ~/.bash_profile
A user's personal startup file. Can be used to extend or override settings in the global configuration script.
Non-Login Shell Session Startup Files: ~/.bashrc
A user's personal startup file. Can be used to extend or override settings in the global configuration script.
alias foo="cd Documents"
A user-defined command called foo which is equivalent to the command "cd Documents".
What is an alias?
A user-defined command.
Synopsis of cat
cat [OPTION]... [FILE]...
cd dir is the same as typing what command?
cd ./dir
Synopsis of cd
cd [directory]
Synopsis of info
info [OPTION]... [MENU-ITEM...]
When a system starts up, the kernel initiates a few of its own activities and launches a program called _____ (parent process) which runs shell scripts (child process) which start all system _____.
init, services
Synopsis of ls
ls [OPTION]... [FILE]...
Octal File Mode: 4
r--
Octal File Mode: 5
r-x
Synopsis of man
man name
Synopsis of mkdir
mkdir [OPTION ...] DIRECTORY ...
Synopsis of sort
sort [OPTION]... [FILE]... sort [OPTION]... --files0-from=F
Synopsis of which
which [filename]...
zip
zip - Package and compress files.
Synopsis of zip
zip [zipfile [file ...]]
top Information Fields: # users
# users are logged in.
top Information Fields: #%ni
#% of the CPU is being used by nice (low-priority) processes.
top Information Fields: #%sy
#% of the CPU is being used for system (kernel) processes.
top Information Fields: #%us
#% of the CPU is being used for user processes (outside of the kernel itself).
Metacharacters: [#-#] (bracket expressions)
- Indicates a # range (i.e. 0-9)
Metacharacters: [character-character] (bracket expressions)
- indicates a character range (i.e. [a-c]zip indicates azip, bzip, or czip).
Octal File Mode: 0
---
Octal File Mode: 1
--x
cut Selection Options: -d delim_char
-d delim_char When -f is specified, use delim_char as the field delimiting character. By default, fields must be separated by a single tab character.
sort Options: -t or --field-separator=char
-t --field-separator=char Define the field-separator character. By default fields are separated by spaces or tabs.
Octal File Mode: 2
-w-
What are the file descriptors for the standard input, output, and error file streams?
0, 1, and 2 respectively.
What four things can commands be?
1. Executable programs 2. Shell built-ins 3. A shell function 4. An alias
find Size units: b
512-byte blocks
cd /path/to/dir is what kind of pathname?
An absolute pathname.
Debian style (.deb)
A packaging system
What is Less?
A pager program (allows for easy viewing of long text documents page by page)
File Type Attributes: -
A regular file.
u+x, go=rw
Add execute permission for the owner and set the permissions for the group and others to read and execute.
Text enclosed in double quotes
All special characters are treated as ordinary characters except $ (dollar sign), \ (blackslash), and ` (back tick). Combines several arguments into one argument.
Command substitution
Allows the use of the output of a commands as an expansion.
Vim - Command mode
Almost every key is a command.
Wildcard: *
Any characters.
Mounting
Attach a device to the filesystem tree.
TAB
Autocompletes an (unique) pathname, variable, username, command, or hostname.
What type of characters should be avoided in filenames?
Avoid punctuation characters and spaces.
/boot
Contains the linux kernel, initial RAM disk image (for drivers needed at boot time), and the boot loader.
/usr/lib
Contains the shared libraries for the programs in /usr/bin.
Backslash escape sequence: \b
Backspace.
rm -i or rm --interactive
Before deleting an existing file, prompt the user for confirmation.
rm -i file1
Before deleting file1, prompt the user for confirmation.
mv -i or mv --interactive
Before overwriting an existing file, prompt the user for confirmation.
cp -i or cp --interactive
Before overwriting an existing file, prompt the user.
Backslash escape sequence: \a
Bell ("alert" - causes the computer to beep).
find File Types: b
Block special device file.
fold -w 12 -s
Break the line at the last available space before the line width is reached.
xargs
Build and execute command lines from standard input
make
Builds a program using the instructions in a Makefile.
sort Options: -b or --ignore-leading-blanks
By default, sorting is performed on the entire line, starting with the first character in the line. This option causes sort to ignore leading spaces in lines and calculates sorting based on the first non-whitespace character on the line.
find Size units: c
Bytes
/usr/sbin
Contains system administration programs.
BSD-style ps Column headers: %CPU
CPU usage as a percent.
cancel
Cancel print jobs.
lprm
Cancel print jobs.
Backslash escape sequence: \r
Carriage return.
Metacharacters: ^ (caret) (anchor)
Cause the match to occur only if the regular expression is found at the beginning of the line (i.e. ^zip).
Metacharacters: $ (dollar sign) (anchor)
Cause the match to occur only if the regular expression is found at the end of the line (i.e. zip$).
Additions to .bashrc: export HISTCONTROL=ignoredups
Causes the shell's history recording feature to ignore a command if the same command was just recorded.
chgrp
Change a file's group ownership.
chmod
Change a file's mode. Can only be used by the file's owner or superuser.
chown
Change a file's owner. Requires superuser privileges.
passwd
Change a user's password.
touch
Change file times
cd
Change the directory (to home directory).
cd -
Change the directory to the previous working directory.
find File Types: c
Character special device file.
POSIX Character Classes: [:xdigit:]
Characters used to express hexadecimal numbers. In ASCII, equivalent to: [0-9A-Fa-f]
Cursor Movement: CTRL-L
Clear the screen and move the cursor to the top left corner. The clear command does the same thing.
clear
Clear the screen.
sort file1.txt file2.txt file3.txt > final_sorted_list.txt
Combine three text files into a single sorted file.
ps: CMD
Command
diff
Compare files line by line
comm
Compares two sorted text files and displays the lines that are unique to each one and the lines they have in common. The first column contains lines unique to the first file argument; the second column, the lines unique to the second file argument; the third column contains the lines shared by both files.
gzip foo.txt
Compress foo.txt to foo.txt.gz
gzip
Compress or expand files.
cat
Concatenate (join) files. Read one or more files and copies them to standard output.
/sbin
Contains "system" binaries.
top Information Fields: hh:mm:ss
Current time of the day.
gzip Options: -d or --decompress or --uncompress
Decompress a file.
join
Data from multiple tables with a shared key field is combined.
dpkg
Debian Package Manager, an installation and packaging tool.
echo "$(cal)"
Displays the calendar formatted correctly (with delimiters) w/o highlighting the current date.
echo $(cal)
Displays the calendar with each text string separated
date
Displays the current date, time, and timezone.
jobs
Displays the current list of jobs.
ls -l "two words.txt"
Displays the long list format of two words.txt.
ls -l two\ words.txt
Displays the long list format of two words.txt.
echo ~username
Displays the name of the home directory of username.
ls -l /bin/usr 2> /dev/null
Dispose of the error message of the ls -l /bin/usr command.
Operator: /
Division (results are integers, regardless if remainders exist).
vim file1 file2 file3...
Edit multiple files at the same time in vim.
echo -e
Enables interpretation of escape sequences.
Dependency resolution
Ensures that when a package is installed, all of its dependencies are installed as well.
Vim - ESC
Enter command mode
Vim - i
Enter insert mode
sudo su
Gain access to superuser privileges
help
Get concise and accurate help for shell builtins.
Package maintainer
Gets software in source code from an upstream provider (the author of the program), compiles it, and creates the package metadata and any necessary installation scripts.
find Size units: G
Gigabytes (units of 1073741824 bytes)
Vim (Global Search-and-Replace Syntax) - g
Global (substitution is performed on every instance of the search string in each line). If g is omitted, only the first instance of the search string on each line is replaced.
find Numeric Argument: +
Greater than
How do you automatically copy text?
Highlight the text in question.
Processes
How Linux organizes the different programs waiting for their turn at the CPU.
Login Shell Session Startup Files: ~/.profile
If neither ~/.bash_profile nor ~/.bash_login is found, bash attempts to read this file.
uniq Options -i
Ignore case during the line comparisons.
uniq Options: -f n
Ignore n leading fields in each line. Fields are separated by whitespace as they are in sort; however, unlike sort, uniq has no option for setting an alternate field separator.
ls -l -h or ls -l --human-readable
In long format listings, display file sizes in human-readable format rather than in bytes.
cat < lazy_dog.txt
Input the text of lazy_dog.txt into the cat command which outputs the text on the screen.
Interpreter
Inputs the program file and reads and executes each instruction contained within it. Each source code instruction is translated every time it is carried out.
Vim (Inserting an Entire File into Another) - r file
Insert an entire file at the cursor location.
Vim - Insert mode
Insert text.
aspell
Interactive spell checker
What is a parent directory?
It is the directory directly above.
cat movie.mpeg.0* > movie.mpeg
Join mpeg files movie.mpeg.001, movie.mpeg.002, movie.mpeg.003, ... into movie.mpeg.
find Tests: -iname pattern
Like the -name test but case insensitive.
find Tests: -type c
Match files of type c.
find Logical Operators: -and
Match if the tests on both sides of the operator are true. May be shortened to -a. Note that when no operator is present, -and is implied by default.
find Size units: M
Megabytes (units of 1048576 bytes)
BSD-style ps Column headers: %MEM
Memory usage as a percent.
Operator: %
Modulo (remainder).
mount
Mount a filesystem. Display a list of the filesystems currently mounted.
Cursor Movement: ALT-B
Move cursor backward one word.
Operator: *
Multiplication
top Information Fields: top
Name of the program.
Backslash escape sequence: \n
Newline.
apt-get
Package handling utility.
How do you paste automatically copied text?
Press the middle mouse button.
lpr
Print files
Less: q
Quit Less.
Process State: R
Running. The process is running or ready to run.
Vim - :ZZ
Save the current file and exit vim.
uniq Options: -s n
Skip (ignore) the leading n characters of each line.
Vim (Replace Confirmation Keys) - n
Skip this instance of the pattern.
sort Options: -r or --reverse
Sort in reverse order. Results are in descending rather than ascending order.
kill -15 or kill -term
Terminate a program.
POSIX Character Classes: [:alpha:]
The alphabetic characters. In ASCII, equivalent to: [A-Za-z].
POSIX Character Classes: [:alnum:]
The alphanumeric characters. In ASCII, equivalent to: [A-Za-z0-9]
ps: TIME
The amount of cpu time consumed by the process.
Environment Variable: PWD
The current working directory.
/root
The home directory for the root account.
What are arguments in commands?
The items upon which the command acts.
POSIX Character Classes: [:lower:]
The lowercase letters.
Pathname expansion
The mechanism by which wildcards work.
Environment Variable: PAGER
The name of the program to be used for paging output. This is often set to /usr/bin/less
POSIX Character Classes: [:digit:]
The numerals zero through nine.
Environment Variable: HOME
The pathname of your home directory.
Environment Variable: OLD_PWD
The previous working directory.
POSIX Character Classes: [:print:]
The printable characters. All the characters in [:graph:] plus the space character.
What are scripts?
They are programs that the system uses.
What do configuration files do?
They contain system settings.
What do options in commands do?
They modify the behavior of the commands.
Vim - u
Undo.
Parameter Expansion
Used to work with variables.
BSD-style ps Column headers: USER
User ID. This is the owner of the process.
ping address
Verify connection to address
ping -c # address
Verify connection to address # times
diff -c file1.txt file2.txt
View the differences between file1.txt and file2.txt in context format.
diff -u
View the differences between files in unified format
Vim (Switching between files) - buffers
View the list of files being edited. Each file has its own buffer #.
kill -28 or kill -winch
Windows change. This is a signal sent by the system when a window changes size. Some programs, like top and less, will respond to this signal by redrawing themselves to fit the new window dimensions.
Are filenames with a period hidden by default?
Yes.
Can multiple short options be strung together?
Yes.
Environment Variable: USER
Your username
Metacharacters: [^characters] (bracket expressions)
^ indicates that the remaining characters are taken to be a set of characters that must not be present at the given character position (i.e. [^bg]zip lists results containing the string "zip" preceded by any character except "b" or "g". Loses its special meaning if its not the first character.
echo a{A{1,2},B{3,4}}b
aA1b, aA2b, aB3b, aB4b
Synopsis of bg
bg [JOBSPEC]
Synopsis of bzip2
bzip2 [OPTION]... [name]...
Synopsis of cal
cal [options] [[month] year]
Synopsis of chgrp
chgrp [OPTION]... GROUP FILE... chgrp [OPTION]... --reference=RFILE FILE...
Synopsis of chmod
chmod [-R] mode file ...
Synopsis of chown
chown [OPTION]... [OWNER][:[GROUP]] FILE... chown [OPTION]... --reference=RFILE FILE...
Synopsis of comm
comm [OPTION]... FILE1 FILE2
What is the form a command is written in?
command -options arguments and/or --options for long options
What is the form multiple commands on one line are written in?
command1; command2; command3
Synopsis of cp
cp [OPTION]... [-T] SOURCE DEST cp [OPTION]... SOURCE... DIRECTORY cp [OPTION]... -t DIRECTORY SOURCE...
Synopsis of df
df [OPTION]... [FILE]...
Synopsis of diff
diff file1 file2
Synopsis of dpkg
dpkg [option...] action
Data stored in the _____ is used by programs to determine facts about our configuration.
environment.
Synopsis of fg
fg [JOBSPEC]
Synopsis of find
find [path...] [expression]
Synopsis of fold
fold [OPTION]... [FILE]...
Synopsis of free
free [options]
Synopsis of grep
grep [OPTIONS] PATTERN [FILE...]
Synopsis of gzip
gzip [OPTION]... [name...]
Synopsis of jobs
jobs [options] [JOBSPEC]
Synopsis of join
join [options] file1 file2
Synopsis of kill
kill [options] <pid> [...]
Synopsis of killall
kill name ...
Synopsis of ln
ln [-fs] source_file target_file ln [-fs] source_file ... target_dir
Synopsis of locate
locate [OPTION]... PATTERN...
Synopsis of mv
mv [OPTION]... [-T] SOURCE DEST mv [OPTION]... SOURCE... DIRECTORY mv [OPTION]... -t DIRECTORY SOURCE...
Synopsis of nl
nl [OPTION]... [FILE]...
Non-login shells inherit the environment from their _____ _____, usually a login shell.
parent process
Synopsis of passwd
passwd [options] [LOGIN]
Synopsis of paste
paste [OPTION]... [FILE]...
Synopsis of ping
ping [-c count] host
Synopsis of printenv
printenv [OPTION]... [VARIABLE]...
Synopsis of ps
ps [options]
Synopsis of rm
rm [OPTION]... FILE...
Octal File Mode: 6
rw-
Octal File Mode: 7
rwx
Synopsis of shutdown
shutdown [options] time (min)
Login and non-login shell sessions read a different set of _____ _____
startup files .
What are abbreviations for standard input, standard output, and standard error?
stdin, stdout, and stderr.
Synopsis of tail
tail [OPTION]... [FILE]...
Synopsis of unzip
unzip file[.zip] [file(s) ...]
Synopsis of type
type [name]...
Synopsis of umask
umask [-S] [mask]
Synopsis of uniq
uniq [OPTION]... [INPUT [OUTPUT]]
Synopsis of uniq .
uniq [OPTION]... [INPUT [OUTPUT]]
Synopsis of vmstat
vmstat [options] [delay [count]]
Synopsis of wc
wc [OPTION]... [FILE]... wc [OPTION]... --files0-from=F
Synopsis of wget
wget [option]... [URL]...
Synopsis of whatis
whatis [name]...
top Information Fields: #%id
#% of the CPU is idle.
top Information Fields: #%wa
#% of the CPU is waiting for I/O
Octal File Mode: 3
-wx
Name three reasons to launch a graphical program from the command line
1. Might not be listed on the window's manager's menu. 2. See error messages. 3. Use cli options
bzip2
A block sorting file compressor.
File Type Attributes: b
A block special file. This file type refers to a device that handles data in blocks, such as a hard drive or CD-ROM drive.
File Type Attributes: c
A character special file. This file type refers to a device that handles data as a stream of bytes, such as a terminal or modem.
Metacharacter
A character that has a special meaning (instead of a literal meaning) to a computer program, such as a shell interpreter.
Operator
A character that represents an action.
Environment Variable: PATH
A colon-separated list of directories that are searched when you enter the name of an executable program.
What is BASH (Bourne Again Shell)?
A common shell program from the GNU Project found on almost all Linux distributions.
Package File
A compressed collection of files that compromise a software package. It may contain programs, data files that support the programs, metadata about the package, and pre- and post-installation scripts that perform configuration tasks before and after package installation.
Process State: Z
A defunct or "zombie" process. This is a child process that has terminated, but has not been cleaned up by its parent.
File Type Attributes: d
A directory.
drwxrwx---
A directory. The owner and the members of the owner group may enter the directory and create, rename, and remove files within the directory.
What is a symbolic link?
A file that references other files.
kill -1 2425 or kill -HUP 2425
A foreground program with PID 2425 running on the terminal will be sent a signal to terminate and the shell indicates that a process received a hangup signal.
Login Shell Session Startup Files: /etc/profile
A global configuration script that applies to all users.
Non-Login Shell Session Startup Files: /etc/bash.bashrc
A global configuration script that applies to all users.
xload
A graphical program that draws a graph showing system load over time.
Processor State: <
A high-priority (not nice) process.
Uniform Resource Identifier (URI)
A label that identifies an abstract or physical resource.
Hostname
A label that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet.
Vim
A lightweight, fast text editor.
diff Context-Format Change Indicators: +
A line added. This line will appear in the second file but not in the first file.
diff Context-Format Change Indicators: !
A line changed. The two versions of the line will be displayed, each in its respective section of the change group.
diff Context-Format Change Indicators: -
A line deleted. This line will appear in the first file but not in the second file.
diff Context-Format Change Indicators: (none)
A line shown for context. It does not indicate a difference between the two files.
Processor State: N
A low-priority (nice) process.
Package Management
A method of installing and maintaining software on the system.
What is an info page?
A more comprehensive alternative to man pages displayed with a reader program (a program that displays info in a website-like manner).
IP (Internet Protocol) address
A number assigned to a device participating in a network that uses the Internet Protocol for communication
ps: PID (Process Identifier)
A number assigned to a process.
What is a relative pathname?
A pathname that begins from the current working directory and uses . (dot) and .. (dot dot) to represent relative positions in the filesystem. . (dot) refers to the working directory and .. (dot dot) refers to the working directory's parent directory.
What is an absolute pathname?
A pathname that begins with the root directory and follows the tree branch by branch until the path to the desired directory or file is completed.
What is a manual (man) page?
A piece of documentation for executable programs displayed with Less.
What is the terminal emulator?
A program that gives access to the shell.
What is the shell?
A program that takes keyboard commands and passes them to the operating system to carry out.
Linker
A program used to form the connections between the output of the compiler and the libraries that the compiled program requires.
Vim (Global Search-and-Replace Syntax) - c
A prompt asking for confirmation for each substitution.
-rwx------
A regular file that is readable, writable, and executable by the file's owner. No one else has any access.
-rwxr-xr-x
A regular file that is readable, writable, and executable by the file's owner. The file may be read and executed by everybody else.
cd ./dir is what kind of pathname?
A relative pathname.
What is a pathname?
A route taken along the filesystem to get to the desired directory.
Library
A shared collection of routines that different programs can use.
Repository
A storage location from which software packages may be retrieved and installed on a computer.
lrwxrwxrwx
A symbolic link with dummy values. The real permissions are kept with the actual file pointed to by the symbolic link.
File Type Attributes: l
A symbolic link. The remaining file attributes are rwxrwxrwx and are dummy values. The real file attributes are those of the file the symbolic link points to.
+x
Add execute permission for the owner, group, and world. Same as a+x.
chmod u+rw
Add read and write permission for the owner.
Operator: +
Addition
paste
Adds one or more columns of text to a file
File descriptor
An abstract indicator used to access a file or other input/output resource, such as a pipe or network connection.
History Expansion
An expansion for items in the history list by using the ! character.
>>
An operator that appends redirected output to a file instead of overwriting the file.
<
An operator that changes the source of stdin from the keyboard to a file.
>
An operator that redirects standard output from the screen to a file.
./configure
Analyze the build environment to produce a Makefile.
Wildcard: [:alpha:]
Any alphabetic character.
Wildcard: [:alnum:]
Any alphanumeric character.
Wildcard: [characters]
Any character that is a member of the set characters.
Wildcard: [[:class:]]
Any character that is a member of the specified class.
Wildcard: [!characters]
Any character that is not a member of the set characters.
Wildcard: BACKUP.[0-9][0-9][0-9]
Any file beginning with BACKUP. followed by exactly three numerals.
Wildcard: Data???
Any file beginning with Data followed by exactly three characters.
Wildcard: [[:upper:]]*
Any file beginning with an uppercase letter.
Wildcard: b*.txt
Any file beginning with b followed by any characters and ending with .txt.
Wildcard: [abc]*
Any file beginning with either a, b, or c.
Wildcard: g*
Any file beginning with g.
Wildcard: *[[:lower:]123]
Any file ending with a lowercase letter or the numerals 1, 2, or 3.
Wildcard: [![:digit:]]*
Any file not beginning with a numeral.
Wildcard: [:lower:]
Any lowercase letter.
Wildcard: [:digit:]
Any numeral.
Wildchard: ?
Any single character.
Wildcard: [:upper:]
Any uppercase letter.
ls -F or ls --classify
Append an indicator name to the end of each listed name (i.e. a forward slash if the name is a directory).
tar Modes: r
Append specified pathnames to the end of an archive.
patch
Apply a diff file to an original
cd ~username
Change the working directory to the home directory of username.
chown [owner] [[:group]] file...
Changes a file' s owner to owner and group owner to group
cd .
Changes directory to working directory.
chown bob:admins foo.txt
Changes the file's owner to bob and group owner to admins.
chown bob: foo.txt
Changes the file's owner to bob and group owner to the login group of user bob.
Vim (Global Search-and-Replace Syntax) - :%s/Line/line/gc
Changes the word Line to line for the entire file (asks for confirmation for each substitution).
cd dir
Changes to a directory called "dir" in the working directory.
cd ..
Changes to the working directory's parent directory.
Makefile
Configuration file that instructs the make program exactly how to build the program.
/dev
Contains a list of device nodes (the devices the kernel understands).
.bash_history
Contains a list of previously used commands.
/lost+found
Contains a partial recovery from a filesystem corruption event.
/proc
Contains a virtual filesystem maintained by the Linux kernel and provides a picture of how the kernel sees the computer.
/etc
Contains all of the system-wide configuration files and a collection of shell scripts that start each of the system services at boot time.
/usr
Contains all the programs and support files used by regular users.
/usr/share
Contains all the shared data used by programs in /usr/bin.
/bin
Contains binaries (programs) that must be present for the system to boot and run.
/opt
Contains commercial software products that may be installed on the system.
/var
Contains data that is likely to change.
/usr/share/doc
Contains documentation of packages installed on the system.
/var/log
Contains log files (records of various system activity).
/media
Contains mount points for removable media such as USB drives, CD-ROMS, etc. that are mounted automatically at insertion.
/usr/local
Contains programs that are not included with the distribution but are intended for system-wide use are installed.
/lib
Contains shared library files used by the core system programs.
/tmp
Contains temporary, transient files created by various programs.
/usr/bin
Contains the executable programs installed by your Linux distribution.
pr
Convert text files for printing
Text Editing: ALT-L
Convert the characters from the cursor location to the end of the word to lowercase.
Text Editing: ALT-U
Convert the characters from the cursor location to the end of the word to uppercase.
Vim (Copying (Yanking) Commands) - y20G
Copes from the current line to the 20th line of the file.
Vim (Copying (Yanking) Commands) - y0
Copies from the current cursor location to the beginning of the line.
Vim (Copying (Yanking) Commands) - y$
Copies from the current cursor location to the end of the current line.
Vim (Copying (Yanking) Commands) - y^
Copies from the current cursor location to the first non-whitespace character in the line.
Vim (Copying (Yanking) Commands) - yG
Copies from the current line to the end of the file.
Vim (Copying (Yanking) Commands) - yW
Copies the current cursor location to the beginning of the next word.
Vim (Copying (Yanking) Commands) - 5yy
Copies the current line and the next four lines.
Vim (Copying (Yanking) Commands) - yy
Copies the current line.
cp -r dir1 dir2
Copy a directory (recursively) into dir2.
cp sourcefile destfile
Copy a file named sourcefile to destfile.
cp dir1/* dir2
Copy all the files in dir1 into dir2.
cp
Copy files and directories.
cp file1 file2 dir
Copy files to a directory.
cp -a or cp --archive
Copy the files and directories and all of their attributes, including ownerships and permissions.
find ~ | wc -l
Counts the number of files in the home directory.
tar czf playground.tgz playground
Create a gzipped archive that contains playground.
ln file link
Create a hard link for the file data file.
ln fun fun-hard
Create a hard link named fun for the fun data file.
ln
Create a hard link.
ln -s file* symlink
Create a symbolic link named symlink for file*
ln -s
Create a symbolic link.
zip -r playground.zip playground
Create a zip file called playground.zip that contains playground.
alias
Create an alias for a command.
tar Modes: c
Create an archive from a list of files and/or directories.
tar cf playground.tar playground
Create an archive that contains playground.
mkdir dir1 dir2 dir3
Create directories dir1, dir2, and dir3
mkdir
Create directories.
vim foo.txt
Create foo.txt using vim.
mkdir -p dir1/dir2
Create nested directories.
ln -s ../fun dir1/funsym
Created a symbolic link named funsym in dir1 for the fun file*.
ls /bin /usr/bin | sort | less
Creates a combined list of all the executable programs in /bin and /usr/bin, put them in sorted order, and then view the list with less.
ls /bin /usr/bin | sort | uniq | less
Creates a combined list of all the executable programs in /bin and /usr/bin, put them in sorted order, removes duplicated lines, and then view the list with less.
ls /bin /usr/bin | sort | uniq | grep zip | less
Creates a combined list of all the executable programs in /bin and /usr/bin, put them in sorted order, removes duplicated lines, print lines with zip, and then view the list with less.
find ~ -type f -name '*.BAK' -delete
Delete files that have the file extension ".BAK" (which is often used to designate backup files) in the home directory (and its subdirectories)
Text Editing: CTRL-D
Delete the character at the cursor location.
Predefined find Actions: -delete
Delete the matching file
Vim (Text Deletion Commands) - dW
Deletes from the current cursor location to the beginning of the next word.
Vim (Text Deletion Commands) - d$
Deletes from the current cursor location to the end of the current line.
Vim (Text Deletion Commands) - d^
Deletes from the current cursor location to the first non-whitespace character in the line.
Vim (Text Deletion Commands) - d20G
Deletes from the current line to the 20th line of the file.
Vim (Text Deletion Commands) - dG
Deletes from the current line to the end of the file.
Vim (Text Deletion Commands) - d
Deletes the current character and places it in a paste buffer.
Vim (Text Deletion Commands) - dd
Deletes the current line.
find File Types: d
Directory.
info
Display a command's info page.
man
Display a command's manual page.
apt-cache show package_name
Display a description of the package.
dpkg -l or dpkg --list
Display a list of all the packages installed on the system.
locate zip | grep bin
Display a list of files with zip and bin in the name.
file
Display brief description of a file* content and filetype.
ls -l -d or ls -l --directory
Display details about the directory rather than its contents.
stat
Display file or file system status
cp -v or cp --verbose
Display informative messages as the copy is performed
cat -A
Display non-printing characters in the output.
ls -l
Display results of the directory's contents in a long format.
top
Display tasks.
free
Display the amount of free memory.
cat ls-output.txt
Display the contents of ls-output.txt.
history
Display the contents of the history list.
pwd
Display the name of the current working directory.
ls -r
Display the results in reverse alphabetical order (ls normally displays results in alphabetical order).
gzip Options: -h or --help
Display usage information.
id
Display user identity.
gzip Options: -v or --verbose
Display verbose messages while compressing.
dpkg --search file_name
Display what package installed file_name
dpkg -s package_name or dpkg --status package_name
Display whether a specified package is installed.
which
Display which executable program will be executed.
dpkg --search /usr/bin/emacs24-x
Display which package installed emacs24-x
cal
Displays a calendar of the current month.
--help
Displays a description of the command's supported syntax and options.
xlogo
Displays a program with the X windows system logo.
history | grep /usr/bin
Displays previous commands used to list /usr/bin.
Scripting/Interpreted Language
Do not require compiling but are executed directly by a special program called an interpreter.
wget http://linuxcommand.org/index.php
Download http://linuxcommand.org/index.php
tload
Draws a graph showing system load over time in the terminal.
sudo
Execute a command as another user.
History: CTRL-O
Execute the current item in the history list and advance to the next one.
Vim - :q
Exit vim.
!#
Expands !# into the contents of the !#th line in the history list.
Operator: **
Exponentiation.
export
Export environment to subsequently executed programs.
cut
Extract a section of text from a line and output the extracted section to standard output.
tar Modes: x
Extract an archive.
cut Selection Options: -f field_list
Extract one or more fields from the line as defined by field_list. The list may contain one or more fields or field ranges separated by commas.
unzip
Extract the contents of a zip file.
tar xf playground.tar
Extract the contents of playground.tar
cut Selection Options: --complement
Extract the entire line of text, except for those portions specified by -c and/or -f.
cut Selection Options: -c char_list
Extract the portion of the line defined by char_list. The list may consist of one or more comma-separated numerical ranges.
Permission Attributes: r
Files: Allows a file to be opened and read. Directories: Allows a directory's contents to be listed if the executable attribute is also set.
File Type Attributes: x
Files: Allows a file to be treated as a program and executed. Program files written in scripting languages must also be set as readable to be executed. Directories: Allows a directory to be entered e.g. cd directory.
File Type Attributes: w
Files: Allows a file to be written to or truncated but not deleted or renamed. Directories: Allows files within a directory to be created, deleted, and renamed if the execute attribute is also set.
command1 | filter | command2
Filter takes the input from command1, changes it, then outputs it. The output is the input for command2 which outputs even more results.
grep -i '^..j.r$' /usr/share/dict/words
Find all the words in the dictionary file that are five letters long and have a j in the third position and an r in the last position while ignoring case.
locate
Find files by name.
grep Options: -h or --no-filename
For multi-file searches, suppress the output of filenames. May also be specified --no-filename.
gzip Options: -f or --force
Force compression even if a compressed version of the original file already exists.
Vim - :q!
Force quit vim.
a2ps
Format files for printing on a Postscript printer
History: ALT-N
Forward search, non-incremental.
chmod -g
Group owner.
find Logical Operators: ( )
Groups tests and operators together to form larger expressions. Since the parentheses characters have special meaning to the shell, escape them with a backlash character
tar Modes: z
Gzip the archive (extensions .tgz or .tar.gz)
gzip Options: -r or --recursive
If one or more arguments on the command line are directories, recursively compress files contained within them.
Login Shell Session Startup Files: ~/.bash_login
If ~/.bash_profile is not found, bash attempts to read this script.
grep -i
Ignore case sensitivity when performing the search.
grep Options: -i or --ignore-case
Ignore case. Do not distinguish between upper and lower case characters. May also be specified --ignore-case.
rm -f or rm --force
Ignore nonexistent files and do not prompt. Overrides the --interactive option.
How are files organized in a hierarchical directory structure?
In a singled root tree-like pattern of directories (folders).
POSIX Character Classes: [:blank:]
Includes the space and tab characters.
dpkg -i package_file or dpkg --install package_file
Install package_file w/o dependency resolution.
apt-get install package_name
Install package_name with dependency resolution.
make install
Install the final product in a system directory (usually usr/local/bin) for use.
ftp
Internet file transfer program
kill -2 or kill -int
Interrupt (terminates) a program. Performs the same function as CTRL-C in the terminal.
CTRL-C
Interrupts (terminates) a program.
grep Options: -v or --invert-match
Invert match. Normally, grep prints lines that contain a match. This option causes grep to print every line that does not contain a match.
Escaping character
Invokes an alternative interpretation on subsequent characters in a character sequence such as \ (backlash).
What does pressing the up-arrow key in the terminal do?
It brings up previously executed commands.
What is the current working directory?
It is the directory in use.
What does pressing the down-arrow key in the terminal do?
It makes the previous command disappear.
What does pressing the left and right arrow keys in the terminal do?
It positions the cursor on the current line.
Vim (Joining Lines Commands) - J
Joins the line below with the line above.
kill -9 or kill -kill
Kernel immediately terminates the process and cannot be ignored (the process doesn't get an opportunity to clean up or save its work).
killall xlogo
Kill all instances of xlogo.
killall -u username
Kill all processes running on username.
killall
Kill processes by name.
Cut and Paste (Kill and Yank) Text: ALT-L
Kill text from the cursor location to the beginning of the current word. If the cursor is at the beginning of a word, kill the previous word.
Cut and Paste (Kill and Yank) Text: ALT-D
Kill text from the cursor location to the end of the current word.
Cut and Paste (Kill and Yank) Text: CTRL-U
Kill text from the cursor location to the end of the current word.
Cut and Paste (Kill and Yank) Text: CTRL-K
Kill text from the cursor location to the end of the line.
find Size units: k
Kilobytes (units of 1024 bytes)
find Numeric Argument: -
Less than
grep Options: -L or --files-without-match
Like the -l option, but print only the names of files that do not contain matches.
jobs .
List active jobs.
ls -a or ls --all
List all files, even those that begin with a period (i.e. hidden).
ps x
List all of our processes.
ps aux
List all processes belonging to every user.
gzip Options: -l or --list
List compression statistics for each file compressed.
echo /usr/*/share
List directories which have the /usr/*/share pattern such as /usr/local/share.
ls
List directory contents.
echo *s
List the contents of a directory ending with s.
echo [[:upper:]]*
List the contents of a directory starting with an uppercase letter.
unzip Options: -l
List the contents of a zip file.
tar Modes: t
List the contents of an archive.
echo *
Lists the contents of a directory (like ls) without coloring scheme.
find ~ \( -type f -not -perm 0600 \) -or \( -type d -not -perm 0700 \)
Look for all the files with permissions that are not 0600 and the directories with permissions that are not 0700.
ind ~ -type f -name "*.JPG" -size +1M
Look for all the regular files that match the wildcard pattern "*.JPG" and are larger than one megabyte
sort Options: -f or --ignore-case
Makes sorting case insensitive.
Metacharacters: [characters] (bracket expressions)
Match a single character from a specified set of characters (i.e. [bg]zip indicates bzip or gzip)
Metacharacters: . (dot) (the any character)
Match any character (i.e. .zip).
find Tests: -empty
Match empty files and directories.
find Tests: -nouser
Match file and directories that do not belong to a valid user. This can be used to find files belonging to deleted accounts or to detect activity by attackers.
find Tests: -group name
Match file or directories belonging to group. group may be expressed as either a group name or as a numeric group ID.
find Tests: -nogroup
Match files and directories that do not belong to a valid group.
find Tests: -newer file
Match files and directories whose contents were modified more recently than the specified file. This is very useful when writing shell scripts that perform file backups. Each time you make a backup, update a file (such as a log), and then use find to determine which files have changed since the last update.
find Tests: -name pattern
Match files and directories with the specified wildcard pattern.
find Tests: -size n or -size +n or -size -n
Match files greater than, less than, or size n.
find Tests: -user name
Match files or directories belonging to user name. The user may be expressed by a username or by a numeric user ID.
find Tests: -perm mode
Match files or directories that have permissions set to the specified mode. mode may be expressed by either octal or symbolic notation.
find Tests: -cmin n or -cmin +n or -cmin -n
Match files or directories whose content or attributes were last modified exactly n minutes ago. To specify less than n minutes ago, use -n and to specify more than n minutes ago, use +n.
find Tests: -ctime n or -ctime +n or -ctime -n
Match files or directories whose contents or attributes were last modified greater than, less than, or n*24 hours ago
find Tests: -cnewer file
Match files or directories whose contents or attributes were last modified more recently than those of file.
find Tests: -mmin n or -mmin +n or -mmin -n
Match files or directories whose contents were last modified greater than, less than, or n minutes ago.
find Tests: -mtime n
Match files or directories whose contents were last modified greater than, less than, or n*24 hours ago.
find Tests: -inum n
Match files with inode number n. This is helpful for finding all the hard links to a particular inode.
find Logical Operators: -or
Match if a test on either side of the operator is true. May be shortened to -o.
find Logical Operators: -not
Match if the test following the operator is false. May be abbreviated with an exclamation point (!).
Cursor Movement: CTRL-B
Move cursor backward one character; same as the left arrow key.
Cursor Movement: CTRL-F
Move cursor forward one character; some as the right arrow key.
Cursor Movement: ALT-F
Move cursor forward one word.
Cursor Movement: CTRL-A
Move cursor to the beginning of the line.
Cursor Movement: CTRL-E
Move cursor to the end of the line.
mv dir1 dir2
Move dir1 (and its contents) into dir2.
mv file1 file2 dir1
Move file1 and file2 into dir1.
mv file1 file2
Move file1 to file2.
mv -i file1 file2
Move file1 to file2. If file2 exists, the user is prompted before it is overwritten.
History: ALT-<
Move to the beginning (top) of the history list.
Less: g
Move to the beginning of the text file.
Less: G
Move to the end of the text file.
History: CTRL-N
Move to the next history entry. Same action as the down arrow.
History: CTRL-P
Move to the previous history entry. Same action as the up arrow.
mv
Move/rename files and directories.
Vim (Moving the Cursor Around) - j or down arrow
Moves cursor down one line.
Vim (Moving the Cursor Around) - CTRL-f or PAGE DOWN
Moves cursor down one page.
Vim (Moving the Cursor Around) - h or left arrow
Moves cursor left one character.
Vim (Moving the Cursor Around) - l or right arrow
Moves cursor right one character.
#-SHIFT-g
Moves cursor to line #
Vim (Moving the Cursor Around) - 0 (zero)
Moves cursor to the beginning of the current line.
Vim (Moving the Cursor Around) - w
Moves cursor to the beginning of the next word or punctuation character.
Vim (Moving the Cursor Around) - W
Moves cursor to the beginning of the next word, ignoring punctuation characters.
Vim (Moving the Cursor Around) - b
Moves cursor to the beginning of the previous word or punctuation character.
Vim (Moving the Cursor Around) - B
Moves cursor to the beginning of the previous word, ignoring punctuation characters.
Vim (Moving the Cursor Around) - $
Moves cursor to the end of the current line.
Vim (Moving the Cursor Around) - ^
Moves cursor to the first non-whitespace character on the current line.
Vim (Moving the Cursor Around) - G
Moves cursor to the last line of the file.
Vim (Moving the Cursor Around) - k or up arrow
Moves cursor up one line.
Vim (Searching Within a Line) - f[character] ENTER ;
Moves the cursor to the next occurrence character.
Are filenames not case sensitive?
No.
wget
Non-interactive network downloader
Where does output go to and input come from normally?
Normally, output goes to the screen and input comes from the keyboard
ls -l two words.txt
Not a valid command due to the space in the filename.
nl
Number lines
cat -n
Number lines in the output.
Non-login shell session
Occurs when we launch a terminal session in the GUI.
Filter: uniq
Omit duplicated lines.
Signals
One of several ways that the OS communicates with programs.
Delimiter
One or more characters that separates text strings such as unquoted spaces, tabs, and newlines.
Login shell session
One which prompts for a username and password.
uniq Options: -d
Only output repeated lines, rather than unique lines.
uniq Options: -u
Only output unique lines. This is the default.
Vim (Opening Additional Files for Editing) - e file
Open an additional file for editing.
Vim (Line Opening Keys) - O
Open the line above the current line.
Vim (Line Opening Keys) - o
Open the line below the current line.
ssh
OpenSSH SSH client (remote login program)
/home
Ordinary users can only write files here (protects the system from errant user activity).
uniq Options: -c
Output a list of duplicate lines preceded by the number of times the line occurs.
Predefined find Actions: -print
Output the full pathname of the matching file to standard output. This is the default action if no other action is specified.
pstree
Outputs a process list arranged in a tree-like pattern showing the parent/child relationships between processes.
vmstat
Outputs a snapshot of a system resource usage including memory, swap, and disk I/O.
Vim (Pasting Commands) - p
Paste the contents of the buffer after the cursor.
Vim (Pasting Commands) - P
Paste the contents of the buffer before the cursor.
patch < diff_file
Patch a file using a diff file.
Package management system: High level tools
Perform metadata searching and dependency resolution (apt-get)
Predefined find Actions: -ls
Perform the equivalent of ls -dils on the matching file. Output is sent to standard output.
Vim (Replace Confirmation Keys) - a
Perform the substitution on this and all subsequent instances of the pattern.
Vim (Replace Confirmation Keys) - y
Perform the substitution.
Vim (Replace Confirmation Keys) - l
Perform this substitution and then quit. Short for last.
sort Options: -n or --numeric-sort
Performs sorting based on the numeric evaluation of a string. Using this option allows sorting to be performed on numeric values rather than alphabetic values.
umask 0000 > foo.txt
Permissions set for foo.txt: -rw-rw-rw-
chmod 777 foo.txt
Permissions set for foo.txt: -rwxrwxrwx
command1 | command2
Pipe the stdout of command1 into the stdin of command2.
| (pipe operator)
Pipe the stdout of one command into the stdin of another.
ls -l /usr/bin | less
Pipe the stdout of the ls -l /usr/bin command into the stdin of the less program.
bg
Place a job in the background (immune from keyboard input and termination.
fg
Place a job in the foreground.
program &
Place a program in the background. Displays a job control number (jobspec) and PID.
grep Options: -n or --line-number
Prefix each matching line with the number of the line within the file.
diff -Naur -r old_file new_file > diff_file
Prepare a diff file. -r is mandatory for directories.
Lossless compression
Preserves all the data contained in the original.
echo '$USER $((2+2)) $(cal)'
Print $USER $((2+2)) $(cal).
echo Five divided by two equals $((5/2))
Print Five divided by two equals 2 (ignoring remainder).
find ~ -type d
Print a list of all the directories in the home directory.
find ~
Print a list of all the files in the home directory
lp
Print files (System V)
find ~ -type f -and -name '*.BAK' -and -print
Print files that have the file extensions ".BAK" in the home directory.
head
Print first (10) lines of a file.
tail
Print last (10) lines of a file.
wc ls-output.txt
Print line, word, and byte counts of ls-output.txt.
wc
Print line, word, and byte counts.
Filter: grep
Print lines matching a pattern.
grep -v
Print lines not matching the pattern.
netstat
Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.
printenv .
Print part or all of the environment.
head -n 5 ls-output.txt
Print the first five lines of ls-output.txt.
tail -n 5 ls-output.txt
Print the last five lines of ls-output.txt.
grep Options: -l or --files-with-matches
Print the name of each file that contains a match instead of the lines themselves.
grep Options: -c or --count
Print the number of matches (or non-matches if the -v option is also specified) instead of the lines themselves.
traceroute
Print the route packets trace to a network host
echo "this is a test"
Print this is a test (with the spaces).
echo with $((5%2)) left over.
Print with 1 left over.
echo $((2+2))
Prints 4.
echo $(((5**2)) * 3))
Prints 75.
echo Number_{1..3}
Prints Number_1, Number_2, Number_3
echo {Z..X}
Prints Z Y X.
printenv
Prints a list of all available variables.
mkdir {2009..2010}-0{1..3}
Prints directories 2009-01, 2009-02, 2009-03, 2010-01,2010-02, 2010-03.
echo $USER
Prints the current username.
echo $(ls)
Prints the output of the ls command
printenv variable
Prints the value of a specific variable.
echo this is a test
Prints this is a test.
Data compression
Process of removing redundancy from data.
Compiling
Process of translating source code (human-readable code) into machine language (binary).
Dependency
Programs usually rely on other software (such as shared libraries) to function.
Environment Variable: PS1
Prompt String 1. This defines the contents of your shell prompt.
Predefined find Actions: -quit
Quit once a match has been made.
Vim (Replace Confirmation Keys) - q or ESC
Quit substituting.
kill -3 or kill -quit
Quit.
Multitasking
Rapidly switching from one executing program to another.
CTRL-D on stdin
Reach end-of-file (EOF).
tee
Reads stdin and copies it to both stdout (allowing data to continue down the pipeline) and to one or more files.
Extended regular expressions (ERE)
Recognizes the following Metacharacters: BRE and ( ) { } ? + |
Basic regular expressions (BRE)
Recognizes the following metacharacters: ^ $ . [ ] *
script
Records an entire shell session and store it in a file
cp -r or cp --recursive
Recursively copy directories and their contents (required when copying directories).
rm -r or rm --recursive
Recursively delete directories.
zip Options: -r
Recursively zip directories
I/O redirection
Redirect the input and output of commands to and from files.
ls -l /usr/bin> ls-output.txt
Redirect the results of the ls -l /usr/bin command to ls-output.txt.
ls -l /bin/usr 2> ls-error.txt
Redirects error of the ls -l /bin/usr command to ls-error.txt.
ls -l /bin/usr &> ls-output.txt
Redirects output and error of the ls -l /bin/usr command to ls-output.txt.
ps: TTY (teletype)
Refers to the controlling terminal for the process.
top Information Fields: load average:
Refers to the number of processes that are in a runnable state and are sharing the CPU. Three values are shown: the first is the average for the last 60 seconds, the next the previous 5 minutes, and finally the previous 15 minutes.
find File Types: f
Regular file
rsync
Remote file and directory synchronization.
chmod u-x
Remove execute permission from the owner.
rm
Remove files and directories.
dpkg -p package_file or dpkg --purge package_file
Remove package file and configuration files.
dpkg -r package_file or dpkg --remove package_file
Remove package_file w/o removing configuration files.
apt-get purge package_name
Remove package_name and configuration files.
apt-get remove package_name
Remove package_name w/o removing configuration files.
Lossy compression
Removes data as the compression is performed, to allow more compression to be applied
History Expansion: !#
Repeat history list item number.
History Expansion: !?string
Repeat last history list item containing string.
History Expansion: !string
Repeat last history list item starting with string.
History Expansion: !!
Repeat the last command. It is the same as pressing the up arrow and ENTER.
ps
Report a snapshot of current processes
uniq -d
Report duplicated lines.
df
Report file system disk space usage
BSD-style ps Column headers: RSS
Resident Set Size. The amount of physical memory (RAM) the process is using in kilobytes.
History: CTRL-R
Reverse incremental search. Searches incrementally from the current command line up the history list.
History: ALT-P
Reverse search, non-incremental. With this key, type the search string and press ENTER before the search is performed.
su
Run a shell as another user.
Less: Page Up or b
Scroll back one page.
Vim (Replace Confirmation Keys) - CTRL-e, CTRL-y
Scroll down and scroll up respectively. Useful for viewing the context of the proposed substitution.
Less: Down Arrow
Scroll down one line.
Less: Page Down or Spacebar.
Scroll forward one page.
Less: Up Arrow
Scroll up one line.
find
Search for files in a directory hierarchy by a variety of attributes.
Vim (Searching the Entire File) - /[characters] ENTER n
Search for the next instance of characters.
Less: n
Search for the next occurrence of the previous search.
Less: /characters
Search forward to the next occurrence of characters.
grep -r
Search through all files in the directory.
grep bzip dirlist*.txt
Searches all of the listed files for the string bzip
kill -11 or kill -segv
Segmentation violation. This signal is sent if a program makes illegal use of memory; that is, it tried to write somewhere it was not allowed to.
kill
Send a signal to a process.
kill [-signal] PID or kill [-signal] jobspec
Send a signal to a specific process. If no signal is specified, then the TERM (Terminate) signal is sent by default. Must be the owner of a process to send a kill command.
ping
Send an ICMP ECHO_REQUEST to network hosts allowing the network connection to be verified.
bg %#
Send job # to the background.
fg %#
Send job # to the foreground.
killall [-u user] [-signal] name...
Send signals to multiple processes matching a specified program or username. Requires superuser privileges.
sort Options: -o or --output=file
Send sorted output to file rather than standard output.
Daemon programs
Services/programs that run in the background w/o an user interface.
gzip Options: -number (1-9)
Set amount of compression. Number is an integer in the range of 1 (fastest, least compression) to 9 (slowest, most compression). The values 1 and 9 may also be expressed as --fast and --best, respectively. The default value is 6.
set
Set shell options. Displays both shell and environment variables.
umask
Set the default file permissions.
go=rw
Set the group owner and anyone besides the owner to have read and write permission. If either the group or world previously had execute permissions, remove them.
What two basic types of data does the shell store in the environment?
Shell variables (bits of data placed there by the bash) and environmental variables (everything else).
ps: STAT
Short for Process state
chmod -a
Short for all; the combination of u, g, and o.
chmod -o
Short for others but means world.
chmod -u
Short for user but means the file or directory owner.
lpq
Show printer queue status information
lpstat
Show printer status information.
top Information Fields: Mem
Shows how physical RAM is being used.
top Information Fields: Swap
Shows how swap space (virtual memory) is being used.
shutdown
Shutdown or reboot the system.
find Tests: -samefile name
Similar to the -inum test. Matches files that share the same inode number as file name.
Mount point
Simply a directory on the filesystem tree for mounting devices or files.
Process State: S
Sleeping. The process is not running; rather, it is waiting for an event, such as a keystroke or network packet.
sort Options: -k or --key=field1[,field2]
Sort based on a key field located from field1 to field2 rather than the entire line.
Filter: sort
Sort lines of text files.
ls -t
Sort results by modification time (most recent files first).
ls -S
Sort results by size (biggest files first).
Vim (Global Search-and-Replace Syntax) - s
Specifies the operation. In this case, substitution (search and replace).
Environment Variable: TZ
Specifies the time zone
fold -w 12 file.txt
Specifiy a line width of 12 characters
tar Modes: f
Specify the name of the tar archive
Vim (Global Search-and-Replace Syntax) - 1,5
Specify the range of lines from line 1 to line 5.
Vim (Global Search-and-Replace Syntax) - 1,$
Specify the range of lines from line 1 to the last line.
Vim (Global Search-and-Replace Syntax) - %
Specify the range of lines from the first line to the last line.
Vim (Global Search-and-Replace Syntax) - :
Starts an ex command (in command mode).
CTRL+Z
Stop a foreground process w/o terminating it.
xlogo CTRL+Z
Stop xlogo
kill -19 or kill -stop
Stop. This signal causes a process to pause w/o terminating. Cannot be ignored.
Process State: T
Stopped. Process has been instructed to stop.
sed
Stream editor for filtering and transforming text
Operator: -
Subtraction
cat -s
Suppress the output of multiple blank lines.
Text enclosed in single quotes
Suppresses all special characters.
sleep 10; echo -e "Time's up\a"
Suspend the computer after 10 minutes. Print Time's up and follow with a beep.
Vim (Switching between files) - N
Switch back to the previous file.
Vim (Switching between files) - n
Switch from one file to the next.
Vim (Switching between files) - buffer #
Switch to the file in buffer #.
find File Types: l
Symbolic link
Regular expressions
Symbolic notations used to identify patterns in text.
Backslash escape sequence: \t
Tab.
Filter
Takes inputs, changes it somehow, then outputs it.
tar
Tape archiving utility.
kill -20 or kill -tstp
Terminal stop. Performs the same function when CTRL-Z is pressed. Unlike the STOP signal, the TSTP signal is received by the program but the program may choose to ignore it.
gzip Options: -t or --test
Test the integrity of a compressed file.
POSIX Character Classes: [:cntrl:]
The ASCII control codes. Includes the ASCII characters 0 through 31 and 127.
Access rights to files are defined in terms of read, write, and execution access for what three types of people?
The file's owner, file's group owner, and everybody else
What is the root directory?
The first directory in the filesystem. It contains files and subdirectories, which contain more files and subdirectories, and so on.
Environment Variable: EDITOR
The name of the program to be used for text editing.
Environment Variable: Display
The name of your display if you are running a graphical environment. Usually this is :O; meaning the first display generated by the X server.
Environment Variable: SHELL
The name of your shell program.
Environment Variable: TERM
The name of your terminal type.
Archiving
The process of gathering up many files and bundling them together into a single large file.
POSIX Character Classes: [:punct:]
The punctuation characters. In ASCII, equivalent to: [-!"#$%&'()*+,./:;<=>?@[\\\]_`{|}~]
su -l user
The resulting shell session is a login session for the specified user (i.e. the user's environment is loaded and the working directory is changed to the user's home directory.)
/
The root directory, where everything begins.
POSIX Character Classes: [:word:]
The same as [:alnum:], with the addition of the underscore (_) character.
Vim (Global Search-and-Replace Syntax) - /Line/line
The search pattern and the replacement text.
POSIX Character Classes: [:upper:]
The uppercase characters
POSIX Character Classes: [:graph:]
The visible characters. In ASCII, it includes characters 33 through 126.
POSIX Character Classes: [:space:]
The whitespace characters including space, tab, carriage return, newline, vertical tab, and form feed. In ASCII, equivalent to: [ \t\r\n\v\f]
What is the shell prompt?
The window that appears when the terminal emulator is launched.
What do wildcards do?
They select filenames based on a pattern of characters.
top Information Fields: Tasks:
This summarizes the number of processes and their various process states.
BSD-style ps Column headers: START
Time when the process started. For values over 24 hours, a date is used.
tr
Translate or delete characters
Text Editing: CTRL-T
Transpose (exchange) the character at the cursor location with the one preceding it.
Text Editing: ALT-T
Transpose the word at the cursor location with the one preceding it.
sort Options: -m or --merge
Treat each argument as the name of a presorted file. Merge multiple files into a single sorted result without performing any additional sorting.
Process State: D
Uninterruptible Sleep. Process is waiting for I/O such as a disk drive.
apt-get update
Update packages.
top Information Fields: h:mm
Uptime (the amount of time since the machine was last booted).
Arithmetic expansion
Use the form $((expression)) to perform mathematical operations. Only supports integers.
Brace expansion
Used to create multiple text strings from a pattern containing braces. It may contain either a comma-separated list of strings or a range of integers or single characters.
tail -f /var/log/messages
View the progress of log files as they are being written in real-time. Press CTRL+C to end the command.
BSD-style ps Column headers: VSZ
Virtual memory size.
cp -u or cp --update
When copying files from one directory to another, copy only files that either don't exist or are newer than the existing corresponding files in the destination directory.
uniq
When given a sorted file (including standard input), it removes any duplicate lines and sends the results to standard output.
mv -u or mv --update
When moving files from one directory to another, move only files that either don't exist in the destination directory or are newer than the existing corresponding files in the destination directory.
Expansion
When something is entered into the terminal, some text is "expanded" into something else before the shell acts upon it.
fold
Wrap each line at a specified length.
Vim - :w file
Write file to hard disk.
gzip Options: -c
Write output to standard output and keep original files. May also be specified with --stdout and --to-stdout.
ls | tee ls.txt | grep zip
Write the directory listing to the file ls.txt before grep filters the pipeline's contents.
ls | tee file
Write the output of the ls command to the screen and to file.
Cut and Paste (Kill and Yank) Text: CTRL-Y
Yank text from the kill-ring (buffer) and insert it at the cursor location.
Synopsis of alias
alias [name=['command']]
Synopsis of apropos
apropos keyword
Synopsis of cut
cut [OPTION]... [FILE]...
Synopsis of date
date [OPTION]... [+FORMAT] date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]
Synopsis of head
head [OPTION]... [FILE]...
Synopsis of help
help name
Synopsis of id
id [OPTION]... [USER]
Synopsis of patch
patch [options] [originalfile [patchfile]]
Synopsis of pstree
pstree [pid, user]
Synopsis of pwd
pwd [OPTION]...
Synopsis of script
script [options] [file]
On startup, the bash reads configuration scripts called _____ _____ which define the default environment shared by all users.
startup files.
Synopsis of su
su [options] [username]
Synopsis of sudo
sudo command
Synopsis of tar
tar [options] [pathname ...]
Synopsis of tee
tee [OPTION]... [FILE]...
