Basic Linux Commands

1. CLI Login terminal: Ctrl-alt-Fn
2. Help
   1. Show help on command (e.g., ls) or configuration file name: man ls
   2. Sometimes need to look in different manual number (e.g., crontab): man 5 crontab
   3. Search help for keyword (e.g., cron): man -k cron
3. Listing directory contents
   1. List directory: ls
   2. Also, if no ls: echo *
   3. List long (permissions, ownership, size, name): ls -l
   4. List all files (including starting with .): ls -a
   5. List long by most to least recent: ls -lt
   6. List with markers for file types: ls -F
   7. Remove default colors on ls: unalias ls

      This will only work for this login session for this user and this environment (and any spawned from it). To make it work for every login for this user, append that line to ~/.bash_profile

4. Directory navigation
   • Relative paths:
     1. Change directory to home: cd ~
     2. Change to specific directory (e.g., public_html): cd public_html
     3. Change to parent directory: cd ..
     4. Change to grandparent directory: cd ../..
     5. Change to current/working directory: cd .
   • Absolute paths:
     1. Change to root directory: cd /
     2. Change to directory in root (e.g., /etc/sysconfig): cd /etc/sysconfig
     3. Show/print working directory: pwd
     4. Remember where you are: pushd .
     5. Return to last pushed directory: popd
5. Bash shell ctrl characters:
   1. Stop/kill current command/program: Ctrl-c
   2. Control scrolling: Ctrl-s to pause, Ctrl-q to resume
   3. Suspend current command/program: Ctrl-z
   4. Resume last suspended program: fg
6. Shell redirection:
   1. <: read from
   2. >: create new or overwrite old
   3. >>: create new or append to existing
7. Standard Files:
   • File numbers and names
     • 0: standard input/stdin
     • 1: standard output/stdout
     • 2: standard error/stderr
   • Examples:
     1. Write 'xyz' to file 'myfile': echo xyz > myfile
     2. Create and/or append to file 'greetings': echo hello >> greetings
     3. Append to file 'greetings': echo world >> greetings

        Check by entering:

        cat greetings
        

     4. Read from file (e.g., .bash_profile): cat < ~/.bash_profile
     5. Suppress all output: cat ~/.bash_profile >/dev/null 2>&1
8. Pipe: |

   Use standard output of command as standard input to another. There can be multiple pipes involved (i.e., each command separated by pipe character).

   Simple example: ls -lt | head

9. Count number of lines (e.g., files): ls -1 | wc -l
10. File operations:
    1. Change ownership: chown user.group file
    2. Change permissions: chmod perms file
11. Make a directory: mkdir testdir
12. Make a directory with intermediate directories: mkdir -p public_html/test
13. Copy files:
    1. Straightforward: cp ~/.bashrc ~/.mybashrc
    2. Copy permissions as well: cp -p ~/.bashrc ~/.mybashrc
    3. Copy recursively (all files and subdirectories): cp -r public_html my_html
14. Move/rename files/directories: mv
15. Remove/delete a file:
    1. Straightforward: rm ~/.mybashrc
    2. Force it (no prompt): rm -f ~/.mybashrc
    3. Force it and recurse for all files and subdirectories (BE CAREFUL): rm -rf my_html
16. Show the first 10 lines of a file or output: dmesg | head
17. Show last 10 lines of a file or output: tail /var/log/secure
18. Show last n lines as the file changes: tail -f /var/log/messages
19. Find a file (e.g., RCS) anywhere: find / -name "RCS" -print
20. Make a symbolic link to a directory or file (ln -s orig new): ln -s /opt/java1.6 /opt/java
21. Use regular expressions to search files (grep):
    1. Find a user name in the password file: grep -i rondeau /etc/passwd
    2. Find something in a directory of files: grep -R localhost /etc
    3. Find something at the start of a line: grep "^root" /etc/passwd
    4. Find something at the end of a line: grep "bash$" /etc/passwd
    5. Find one of two things: grep "(root|nobody)" /etc/passwd
22. Show how much space on file systems in human-readable form: df -h
23. Show all processes (useful piped to grep): ps auxwww
24. Show who is logged on: who