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
