Linux-Commands

System Commands

   $ uname –a - display linux system information 
   $ uname –r - display kernel release information 
   $ uptime - show how long system running + load 
   $ hostname - show system host name 
   $ hostname -i - display the IP address of the host 
   $ last reboot - show system reboot history 
   $ date - show the current date and time 
   $ cal - show this month calendar 
   $ w - display who is online
   $ whoami - who you are logged in as 
   $ finger user - display information about user

Hardware related

   $ dmesg - detected hardware and boot messages 
   $ cat /proc/cpuinfo - CPU model 
   $ cat /proc/meminfo - hardware memory 
   $ cat /proc/interrupts - lists the number of interrupts per CPU per I/O device 
   $ lshw - displays information on hardware configuration of the system 
   $ lsblk - displays block device related information in Linux 
   $ free -m - used and free memory (-m for MB)
   $ lspci -tv - show PCI devices 
   $ lsusb -tv - show USB devices 
   $ lshal - show a list of all devices with their properties 
   $ dmidecode - show hardware info from the BIOS
   $ hdparm -i /dev/sda -show info about disk sda 
   $ hdparm -tT /dev/sda - do a read speed test on disk sda 
   $ badblocks -s /dev/sda - test for unreadable blocks on disk sda

Statistics and Analyze

   $ top - display and update the top cpu processes
   $ mpstat 1 - display processors related statistics 
   $ vmstat 2 - display virtual memory statistics 
   $ iostat 2 - display I/O statistics (2sec Intervals)
   $ tail -n 500 /var/log/syslog - last 10 kernel/syslog messages
   $ tcpdump -i eth1 - capture all packets flows on interface eth1 
   $ tcpdump -i eth0 'port 80' - monitor all traffic on port 80 ( HTTP ) 
   $ lsof - list all open files belonging to all active processes
   $ lsof -u testuser - list files opened by specific user 
   $ free –m - show amount of RAM 
   $ watch df –h - watch changeable data continuously

Users

   $ id - show the active user id with login and group
   $ last - show last logins on the system 
   $ who - show who is logged on the system
   $ groupadd admin - add group "admin" (force add existing group) 
   $ useradd -c "Joe Smith" -g admin -m joe - Create user "joe" and add to group "admin"
   $ userdel joe - delete user joe (force,file removal) 
   $ adduser joe - add user "joe" 
   $ usermod - modify user information

File Commands

   $ ls –al - display all information about files / directories
   $ ls -alR - display all information about files / directories recursively
   $ pwd - show current directory path
   $ mkdir directory-name - create a directory
   $ rm file-name - delete file
   $ rm -r directory-name - delete directory recursively 
   $ rm -f file-name - forcefully remove file 
   $ rm -rf directory-name - forcefully remove directory recursively 
   $ cp file1 file2 - copy file1 to file2 
   $ cp -r dir1 dir2 - copy dir1 to dir2, create dir2 if it doesn’t exist 
   $ mv file1 file2 - move files from one place to another
   $ ln –s /path/to/file-name link-name - create symbolic link to file-name
   $ touch file - create or update file 
   $ cat > file - place standard input into file
   $ more file - output the contents of file 
   $ head file - output the first 10 lines of file
   $ tail file - output the last 10 lines of file
   $ tail -f file - output the contents of file as it grows starting with the last 10 lines 
   $ gpg -c file - encrypt file
   $ gpg file.gpg - decrypt file

Process Related

   $ ps - display your currently active processes
   $ ps aux | grep 'telnet' - find all process id related to telnet process 
   $ pmap - memory map of process 
   $ top - display all running processes 
   $ kill pid - kill process with mentioned pid id
   $ killall proc - kill all processes named proc 
   $ pkill processname - send signal to a process with its name 
   $ bg - resumes suspended jobs without bringing them to foreground 
   $ fg - brings the most recent job to foreground 
   $ fg n - brings job n to the foreground

File Permission Related

   $ chmod octal file-name - change the permissions of file to octal , which can be found separately for user, group and world; octal value 4 -read 2 –write 1 –execute
   $ chown owner-user file - change owner of the file 
   $ chown owner-user:owner-group file-name - change owner and group owner of the file 
   $ chown owner-user:owner-group directory - change owner and group owner of the directory

Keyboard shortcuts

   Alt+Ctrl+T - open Terminal Window

   Alt+Ctrl+L - lock the screen
   Alt+Ctrl+Del - logoff

   Alt+F4 - close current window
   Alt+F2 - pop up command window (for quickly running commands)

   Super-W  - show all windows in the current workspace
   Ctrl+Super+D - show desktop

   Ctrl+A - select all items on list or text
   Ctrl+C - copy all selected items to clipboard
   Ctrl+X - cut all selected items to clipboard
   Ctrl+V or Mouse middle button click - paste all selected items to clipboard

   PrintScr - takes screenshot
   Alt+PrintScr - takes screenshot of windows
   Shift+PrintScr - takes screenshot of selected window area