The 15 Most Useful Linux commands

Learning Linux or UNIX is a seemingly daunting task, there are thousands of commands out there, each with hundreds of options. But in reality you only need to know a few of them.

I use unix quite a bit, usually either on one of our Linux servers, or on my Mac with OS X (a unix based operating system). And these are the 15 commands that I use most. If you can memorize these 15 commands, you can do quite a bit on a unix operating system, and add unix as a skill on your resume.

The 15 Most Important UNIX commands

1. man - show manual for a command, example: man ls hit q to exit the man page.
2. cd - change directory, example: cd /etc/
3. ls - list directory, similar to dir on windows. example: ls /etc, use ls -l /etc to see more detail
4. cp - copy a file or directory, example: cp source dest if you want to copy a directory use the -R option for recursive: cp -R /source /dest
5. mv - move a file, example: mv source dest
6. rm - remove a file, example: rm somefile to remove a directory you may need the -R option, you can also use the -f option which tells it not to confirm each file: rm -Rf /dir
7. cat - concatenate, or output a file cat /var/log/messages
8. more - outputs one page of a file and pauses. example: more /var/log/messages press q to exit before getting to the bottom. You can also pipe to more | more from other commands, for example ls -l /etc | more
9. scp - secure copy, copies a file over SSH to another server. example: scp /local/file user@host.com:/path/to/save/file
10. tar - tape archiver, tar takes a bunch of files, and munges them into one .tar file, the files are often compressed with the gzip algorithm, and use the .tar.gz extension. to create a tar tar -cf archive.tar /directory, then to extract the archive to the current directory run tar -xf archive.tar to use gzip, just add a z to the options, to create a tar.gz: tar -czf archive.tar.gz /dir to extract it tar -xzf archive.tar.gz
11. grep - pattern matcher, grep takes a regular expression, or to match a simple string you can use fast grep, fgrep failure /var/log/messages, I'm usually just looking for a simple pattern so I tend to use fgrep more than regular grep. Grep is case sensitive by default, but here's how you can do case insensitive grep.
12. find - lists files and directories recursively on a single line, I usually pipe grep into the mix when I use find, eg: find / | fgrep log
13. tail - prints the last few lines of a file, this is handy for checking log files tail /var/log/messages if you need see more lines, use the -n option, tail -n 50 /var/log/messages you can also use the -f option, which will continuously show you the end of the file as things are added to it (very handy for watching logs) tail -f /var/log/messages
14. head - same as tail, but shows the first few lines the file
15. vi - text editor, there are several text editors such as emacs, and nano, but vi is usually installed on any server so its a good one to learn. To edit a file type vi file_name.txt to edit a line press Esc i then to save changes and exit use Esc wq, or to quit without saving use Esc q!. There are a million other commands, but that will enable you to edit files at a basic level.

Once you learn these commands, and are comfortable with them, you shouldn't stop there, there are lots of other commands that can make your life easier.

Runner Up Essential Commands

When I first posted this in 2005, I had quite a few comments suggesting some commands I was missing, here's a list for you:

• chmod - change file permissions
• chown - change file owner user and file group
• ln - create a symbolic link - kind of like a virtual file or folder.
• less - some are saying that less is more, less is the opposite of the more command
• ps - show running processes, along with top it these commands are the task manager for linux or unix based systems.
• wc - word count, this can be useful for counting things in the output, for example to count the number of files in a directory on linux.

Did I miss any commands that you think are essential to using a UNIX or Linux based operating system?