Getting started with UNIX - Basic commands

List of basic commands of unix

reboot - Immediately stops all running processes, shuts down the system, then reboots.

sudo - Runs commands as root, which means no limitations due to permissions.

shutdown - Stops all running processes and shuts down the system.
Parameters can be specified to issue a delayed shutdown or a shutdown at a particular time.

date - Prints out the current system date and time.
Specified parameters can change the format of the output.

df - Reports the disk space usage for the file system.

hostname - Displays the name of the current host system.

ps - Displays information about all of the processes currently running on the system.

du - Disk usage

ps - List running processes

To know the process id of a process running

 ps -elf | grep process_name

 ps -fA | grep process_name

| -> pipe character is very useful for redirecting output of one command to other

 grep is used to find the pattern

To create a file

 cat filename

 touch filename

To search something in a file

 grep -i thing_to_be_searched filename

To search something across directories

 grep -rn pattern_to_be_searched directory_starting_from_where_search_to_be_started 

To view processes along with the memory they are consuming run

 top

Ctrl + M will sort in decreasing order of memory consumption

chmod / chown - Changes the access permissions of one or more files (chmod) or
changes the ownership of a particular file to a new user (chown).
Only users with permission or ownership of a file can change that file’s permissions or ownership.

chown owner_name filename

chmod 755 filename  

Here 7 is the permission for owner

5 and 5 for group and others respectively

7 - xrw

5 - xr

2-r

4-x

1-w

Access permissions are of three types

 x Execute permissions (4)

 r Read permission (2)

 w write permissions (1)

Aur linux has concept of owner, group and others.

Owner is the owner of the file

Every file or directory belong to a group

And third is others(not owner and not belonging to the group of the file)

Permissions are in the order Owner permissions Group permissions  others permissions