Unix 1: Commands, directories, and processes

absolute path

A path to a directory that has a constant startpoint (the root)

relative path

A path to a directory that is in relation to your current location

-rw-r--r--

Access rights to the file Leading dash is regular file, d is a directory. next three are for file owners, next three group rights, next three is everyone else.

ls -F

Appends an indicator character to each listed name.

Pressing tab while entering a directory name

Autofills the directory name up until the names differ

BSD

Berkeley Software Distribution. UC Berkeley's distribution of the Unix operating system. One of the most popular.

sort

Concatenates files based on a designated sort key

ctrl+c

Conrol Break

/bin

Contains binaries (programs) that must be present for the system to boot and run.

/usr/sbin

Contains more system administration programs.

/lib

Contains shared library files used by the core system programs. These are similar to DLLs in Windows.

/boot

Contains the Linux kernel, initial RAM disk image, and the boot loader

cp

Copy files and directories

ln

Create hard and symbolic links

whatis

Display a very brief description of a command

type *command*

Displays the kind of command the shell will execute given the *command*

*command*--help

Displays usage information for the command given. available for many executables.

/lost+found

Each formatted partition or device using a Linux file system, such as ext3, will have this directory. It is used in the case of a partial recovery from a file system corruption event. Unless something really bad has happened to your system, this directory will remain empty.

ps -f

Gives a full format columned listing of processes

/home

In normal configurations, each user is given a directory here. Ordinary users can only write files in these directories. This limitation protects the system from errant user activity.

ls -A

Like the -a option except it does not list . (current directory) and .. (parent directory)

ls -l

List all files and dirctories as well as their creation info

ls -a

List all files and directories including those hidden by a .

ls -S

List all files and directories sorted by file size

ls -lt

List files and directories by date created

who

List users currently logged in

/usr/share/doc

Most packages installed on the system will include some kind of documentation. In this directory, we will find documentation files organized by package.

cd ..

Move up one directory

/media

On modern Linux systems this directory will contain the mount points for removable media such as USB drives, CD-ROMs, etc. that are mounted automatically at insertion.

/mnt

On older Linux systems, this directory contains mount points for removable devices that have been mounted manually.

head

Output the first part of a file

tail

Output the last part of a file

grep

Print lines matching a pattern

wc

Print newline, word, and byte counts for each file

PID #

Process Identification Number

PPID

Process Parent ID. The parent command of the spawned process

vi, :q

Quit the VI editor

tee

Read From Stdin And Output To Stdout And Files

rm

Remove files and directories

ps

Reports a snapshot of current processes

apropos *search term*

Searches the list of man pages for possible matches based on a search term

w

Shows current logged in users

history

Shows prior commands entered

top

Shows system usage. Default is similar to Task Manager

man ls

Shows the manual page for the referenced command

cd !$

Stores the value f the at command in the variable. Thus allowing a cd into a previous mkdir

Less is more

The less command is a more sophisticated version of the more command

/

The root directory

/usr/lib

The shared libraries for the programs in /usr/bin.

/sbin

This directory contains "system" binaries. These are programs that perform vital system tasks that are generally reserved for the superuser

/usr/share

This directory contains all the shared data used by programs in /usr/bin. This includes things like default configuration files, icons, screen backgrounds, sound files, etc.

/var/log

This directory contains log files, records of various system activity. These are very important and should be monitored from time to time. The most useful ones are /var/log/messages and/or /var/log/syslog. Note that for security reasons on some systems, you must be the superuser to view log files.

/tmp

This directory is intended for storage of temporary, transient files created by various programs. Some configurations cause this directory to be emptied each time the system is rebooted.

/proc

This directory is special. It's not a real file system in the sense of files stored on your hard drive. Rather, it is a virtual file system maintained by the Linux kernel. The "files" it contains are peepholes into the kernel itself. The files are readable and will give you a picture of how the kernel sees your computer.

/opt

This directory is used to install "optional" software. This is mainly used to hold commercial software products that may be installed on your system.

/usr

This directory tree is likely the largest one on a Linux system. It contains all the programs and support files used by regular users.

/dev

This is a special directory which contains device nodes. "Everything is a file" also applies to devices. Here is where the kernel maintains a list of all the devices it understands.

/root

This is the home directory for the root account.

/usr/local

This tree is where programs that are not included with your distribution but are intended for systemwide use are installed. Programs compiled from source code are normally installed in /usr/local/bin. On a newly installed Linux system, this tree exists, but it will be empty until the system administrator puts something in it.

alias e.g. alias foo='cd /usr; ls; cd -'

Used to create your own command

chmod

Used to determine permissions to a directory. Based around the number 7. 1 is execute, 2 is write, 4 is read. Adding the numbers gives you the number relevant to the permissions you want.

tar

Utility for collecting many files into one archive file

/var

With the exception of /tmp and /home, the directories we have looked at so far remain relatively static, that is, their contents don't change. This directory tree is where data that is likely to change is stored. Various databases, spool files, user mail, etc. are located here.

cat

allows the creation of single or multiple files, view contents of a file, concatenate files and redirect the output in terminal or files

cd

change directory

cd ~user_name

changes the working directory to the home directory of user_name.

which

displays an executable's location

df

displays free disk space on your drives

vi :q!

exit the vi editor without saving any changes

ls

list files and directories

mkdir

make directory

mv

move/rename files and directories

pwd

print working directory (Shows where you are)

uniq

report or omit repeated lines

ls -lt --reverse

reverses the order of the sort

free

shows amount of free memory

ls --help

shows information about the ls command. ls can be replaced by any command

/usr/bin

this contains the executable programs installed by your Linux distribution. It is not uncommon for this directory to hold thousands of programs.

/etc

this directory contains all of the system-wide configuration files. It also contains a collection of shell scripts which start each of the system services at boot time. Everything in this directory should be readable text.