Common SSH Commands and Linux Shell Commands

We’ve put together some of the more frequently used SSH commands or 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 SSH commands or 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.

    Common SSH Commands or 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

    cat filename.txt : cat the contents of filename.txt to your screen

    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 : 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 to go to the
    next page, to quit

    pico : friendly, easy to use file editor
    pico /home/burst/public_html/index.html : edit the index page for the user’s
    website.

    vi : another editor, tons of features, harder to use at first than pico
    vi /home/burst/public_html/index.html : edit the index page for the user’s website.

    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

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

    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 orginal, however you can delete
    the link and it will not delete the original.

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

    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.

    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!

    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.

    kill: terminate a system process
    kill -9 PID EG: kill -9 431
    kill PID EG: kill 10550
    Use top or ps ux to get system PIDs (Process IDs)

    EG:
    PID TTY TIME COMMAND
    10550 pts/3 0:01 /bin/csh

    10574 pts/4 0:02 /bin/csh

    10590 pts/4 0:09 APP

    Each line represents one process, with a process being loosely defined as a
    running instance of a program. The column headed PID (process ID) shows the
    assigned process numbers of the processes. The heading COMMAND shows the location
    of the executed process.

    Putting commands together
    Often you will find you need to use different commands on the same line. Here
    are some examples. Note that the | character is called a pipe, it takes date
    from one program and pipes it to another.
    > means create a new file, overwriting any content already there.
    >> means tp append data to a file, creating a newone if it doesn not already
    exist.
    < send input from a file back into a command.

    grep User /usr/local/apache/conf/httpd.conf |more
    This will dump all lines that match User from the httpd.conf, then print the
    results to your screen one page at a time.

    last -a > /root/lastlogins.tmp
    This will print all the current login history to a file called lastlogins.tmp
    in /root/

    tail -10000 /var/log/exim_mainlog |grep domain.com |more
    This will grab the last 10,000 lines from /var/log/exim_mainlog, find all occurances
    of domain.com (the period represents ‘anything’,
    — comment it out with a so it will be interpretted literally), then send it
    to your screen page by page.

    netstat -an |grep :80 |wc -l
    Show how many active connections there are to apache (httpd runs on port 80)

    mysqladmin processlist |wc -l
    Show how many current open connections there are to mysql

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