linux_tutorial.md

Useful Linux Commands

Check filesize

ls -l --block-size=M <filepath>

CPU Usage and Running Process

top

Press 'i' to off the idle process visibility, 'M' for sort the processes in memory usage, 'S' for running time.

htop

ps aux | grep -i anirban

The advantage of ps command is one can easily find processes associated with the term anirban

pidof anirban

pgrep anir

The commands like top and ps help to find all the running and idle processes in your system. If you happen to know the process name (or part of a process name), you can use pidof (pgrep) command.

Kill a process

kill -9 <process_id>

You can use -9 or -SIGKILL to kill the process immediately. If you dont write any of these flags, the system uses SIGTERM(15) by default.

System configuration

sudo lshw -short

To check cpu configurations: lscpu

To check storage services: lsblk

File Permissions

Enable/Disable users from accessing files

A file may have three types of permission: read ('r'), write ('w'), and execute ('x'). Each permission may be 'on' or 'off' for each of three categories of users: the file's owner; other people in the same group as the owner; and all others. To find out a file's mode, or permission settings, use the command ls -l filename. The output will be of the form:

-rwxr-x--x 1 owner 2300 Jul 14 14:38 filename

The string of 10 characters at the left shows the mode. The initial '-' indicates that the file is a plain file; a 'd' would indicate a directory. Characters 2-4 are, respectively, 'r', 'w', or 'x' if the corresponding permission is turned on for the owner or '-' if the permission is turned off. Characters 5-7 similarly show the permissions for the group; characters 8-10 for all others.

Change mode of a file/directory

To change the mode of a file, use the chmod command. The general form is:

chmod X@Y <file1> <file2> ...

where X is any combination of the letters 'u' (for owner), 'g' (for group), 'o' (for others), 'a' (for all; that is, for 'ugo'); @ is either '+' to add permissions, '-' to remove permissions, or '=' to assign permissions absolutely; and Y is any combination of 'r', 'w', 'x'. Examples:

To deny rwx permission for group and others - chmod go-rwx <file/dir>

Full details : https://statistics.berkeley.edu/computing/unix-permissions