Linux/Unix commands

File Commands

1. ls Directory listing
2. ls -al Formatted listing with hidden files
3. ls -lt Sorting the Formatted listing by time modification
4. cd dir Change directory to dir
5. cd Change to home directory
6. pwd Show current working directory
7. mkdir dir Creating a directory dir
8. cat >file Places the standard input into the file
9. more file Output the contents of the file
10. head file Output the first 10 lines of the file
11. tail file Output the last 10 lines of the file
12. tail -f file Output the contents of file as it grows,starting with the last 10 lines
13. touch file Create or update file
14. rm file Deleting the file
15. rm -r dir Deleting the directory
16. rm -f file Force to remove the file
17. rm -rf dir Force to remove the directory dir
18. cp file1 file2 Copy the contents of file1 to file2
19. cp -r dir1 dir2 Copy dir1 to dir2;create dir2 if not present
20. mv file1 file2 Rename or move file1 to file2,if file2 is an existing directory
21. ln -s file link Create symbolic link link to file

Process management

1. ps To display the currently working processes
2. top Display all running process
   Unix/Linux Command Reference 
3. kill pid Kill the process with given pid
4. killall proc Kill all the process named proc
5. pkill pattern Will kill all processes matching the pattern
6. bg List stopped or background jobs,resume a stopped job in the background
7. fg Brings the most recent job to foreground
8. fg n Brings job n to the foreground

File permission

1. chmod octal file Change the permission of file to octal,which can be found separately for user,group,world by adding, • 4-read(r) • 2-write(w) • 1-execute(x)
   Searching 1. grep pattern file Search for pattern in file
2. grep -r pattern dir Search recursively for pattern in dir
3. command | grep pattern Search pattern in the output of a command
4. locate file Find all instances of file
5. find . -name filename Searches in the current directory (represented by a period) and below it, for files and directories with names starting with filename 6. pgrep pattern Searches for all the named processes , that matches with the pattern and, by default, returns their ID

System Info

1. date Show the current date and time
2. cal Show this month’s calender
3. uptime Show current uptime
4. w Display who is on line
5. whoami Who you are logged in as Unix/Linux Command Reference 
6. finger user Display information about user
7. uname -a Show kernel information
8. cat /proc/cpuinfo Cpu information
9. cat proc/meminfo Memory information
10. man command Show the manual for command
11. df Show the disk usage
12. du Show directory space usage
13. free Show memory and swap usage
14. whereis app Show possible locations of app
15. which app Show which applications will be run by default

Compression

1. tar cf file.tar file Create tar named file.tar containing file
2. tar xf file.tar Extract the files from file.tar
3. tar czf file.tar.gz files Create a tar with Gzip compression
4. tar xzf file.tar.gz Extract a tar using Gzip
5. tar cjf file.tar.bz2 Create tar with Bzip2 compression
6. tar xjf file.tar.bz2 Extract a tar using Bzip2
7. gzip file Compresses file and renames it to file.gz
8. gzip -d file.gz Decompresses file.gz back to file

Network

1. ping host Ping host and output results
2. whois domain Get whois information for domains
3. dig domain Get DNS information for domain
4. dig -x host Reverse lookup host
5. wget file Download file
6. wget -c file Continue a stopped download

Shortcuts

1. ctrl+c Halts the current command
2. ctrl+z Stops the current command, resume with fg in the foreground or bg in the background
3. ctrl+d Logout the current session, similar to exit
4. ctrl+w Erases one word in the current line
5. ctrl+u Erases the whole line
6. ctrl+r Type to bring up a recent command
7. !! Repeats the last command
8. exit Logout the current session