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tutorials:unix_commands

Shell Commands

We've put together some of the more frequently used linux shell commands, and organized them by name so you can easily find a command, their description and how to use it. This guide will continue to be updated and should not be considered a complete list of linux shell commands, but commands, we found, often used. If you would like to add to this guide, please email us and let us know. We know that these themselves are bash commands and not actually SSH commands but it is what most Linux newbies are looking for when searching for 'SSH commands'.

Common Linux Shell Commands

ls

List files/directories in a directory, comparable to dir in windows/dos.

ls -al
#shows all files (including ones that start with a period), directories, and details attributes for each file.

cd

Change directory ·· cd /usr/local/apache : go to /usr/local/apache/ directory

cd ~  #go to your home directory 
cd -  #go to the last directory you were in
cd .. #go up a directory cat : print file contents to the screen

chmod

Changes file access permissions.

The set of 3 go in this order from left to right: USER - GROUP - EVERYONE

0 = --- No permission
1 = --x Execute only
2 = -w- Write only
3 = -wx Write and execute
4 = r-- Read only
5 = r-x Read and execute
6 = rw- Read and write
7 = rwx Read, write and execute

Usage: chmod numberpermissions filename/directory

chmod 000  #No one can access 
chmod 644  #Usually for HTML pages
chmod 755  #Usually for CGI scripts

chown

Changes file ownership permissions

The set of 2 go in this order from left to right: USER - GROUP

chown root myfile.txt       # Changes the owner of the file to root
chown root.root myfile.txt  # Changes the owner and group of the file to root

tail

Like cat, but only reads the end of the file.

tail /var/log/messages      # see the last 20 (by default) lines of /var/log/messages 
tail -f /var/log/messages   # watch the file continuously, while it's being updated 
tail -200 /var/log/messages # print the last 200 lines of the file to the screen

more/less

like cat, but opens the file one screen at a time rather than all at once

more /etc/userdomains # browse through the userdomains file. hit Space to go to the next page, q to quit

vi

vi /home/burst/public_html/index.html # edit the index page for the user's website

While in the vi program you can use the following useful commands, you will need to hit SHIFT + : to go into command mode

:q! # This force quits the file without saving and exits vi
:w  # This writes the file to disk, saves it
:wq # This saves the file to disk and exists vi
:LINENUMBER : EG :25 # Takes you to line 25 within the file
:$ # Takes you to the last line of the file
:0 # Takes you to the first line of the file

grep

Looks for patterns in files

grep root /etc/passwd    # shows all matches of root in /etc/passwd
grep -v root /etc/passwd # shows all lines that do not match root

ln

Create's “links” between files and directories

ln -s /usr/local/apache/conf/httpd.conf /etc/httpd.conf # Now you can edit /etc/httpd.conf rather than the original. changes will affect the original, however you can delete the link and it will not delete the original.

last

Shows who logged in and when

last -20    # shows only the last 20 logins 
last -20 -a # shows last 20 logins, with the hostname in the last field 

w

shows who is currently logged in and where they are logged in from.

who # This also shows who is on the server in an shell

netstat

shows all current network connections.

netstat -an # shows all connections to the server, the source and destination ips and ports.
netstat -rn # shows routing table for all ips bound to the server.

top

shows live system processes in a nice table, memory information, uptime and other useful info. This is excellent for managing your system processes, resources and ensure everything is working fine and your server isn't bogged down. top then type Shift + M to sort by memory usage or Shift + P to sort by CPU usage

ps

ps is short for process status, which is similar to the top command. It's used to show currently running processes and their PID. A process ID is a unique number that identifies a process, with that you can kill or terminate a running program on your server (see kill command).

ps U username # shows processes for a certain user
ps aux # shows all system processes
ps aux --forest # shows all system processes like the above but organizes in a hierarchy that's very useful!

touch

creates an empty file

touch /home/burst/public_html/404.html # create an empty file called 404.html in the directory /home/burst/public_html/ 

file

attempts to guess what type of file a file is by looking at it's content.

file * # prints out a list of all files/directories in a directory

du

shows disk usage.

du -sh # shows a summary, in human-readble form, of total disk space used in the current directory, including subdirectories.
du -sh * # same thing, but for each file and directory. helpful when finding large files taking up space. 

wc

word count

wc -l filename.txt # tells how many lines are in filename.txt

cp

copy a file

cp filename filename.backup # copies filename to filename.backup
cp -a /home/burst/new_design/* /home/burst/public_html/ # copies all files, retaining permissions form one directory to another. 
cp -av * ../newdir # Copies all files and directories recurrsively in the current directory INTO newdir

mv

move a file command

mv -v oldfilename newfilename # Move a file or directory from oldfilename to newfilename in a verbose mode

rm

delete a file

rm -vi filename.txt # deletes filename.txt, will more than likely ask if you really want to delete it
rm -fv filename.txt # deletes filename.txt, will not ask for confirmation before deleting.
rm -rfv tmp/ # recursively deletes the directory tmp, and all files in it, including subdirectories. 
             # BE VERY CAREFULL WITH THIS COMMAND!!!

tar

creating and Extracting .tar.gz and .tar files

tar -zxvf file.tar.gz         # Extracts the file that have been compressed
tar -xvf file.tar             # Extracts the file
tar -cf archive.tar contents/ # Takes everything from contents/ and puts it into archive.tar
gzip -d filename.gz           # Decompress the file, extract it
tutorials/unix_commands.txt · Last modified: 2016/03/27 21:27 by Richard.Randriatoamanana@ec-nantes.fr