Linux – program return code.

Written by kisa

On May 17, 2020

And , or , does not matter…

Return code of a given program is 0 if everything went OK and Not Zero if something went south.

logical and &&

$ls -l someFileOrDir && echo OK

logical or ||

$ls -l  nonExistedFile || echo ERR

whenever a program returns Zero a command stops executing, In every other case bash will continue to execute the rest of the line.

does not matter ;

in any case continue the execution:

$ls -lia ; echo hello ; mkdir new_dir

By adding ; between commands we can concatenate multiple instruction in one line without considering the return code of any given part of the instruction.


Static file system information (such as file system/mount point/type/options/dump/pass) are located in


to check UID use

$lsblk -o UUID


$grep UUID /etc/fstab

$lsblk -o UUID /dev/vda1

To check free space, total space and other drive info use

$df -h


to see even more information use 


you can use (slink) at

$ls -l /etc/mtab

that points at 

$ls -l /proc/self/mounts

and another (slink) that points to self/mounts

$ls -l /proc/mounts

All commands above are “unlocked” to all linux users.

But to mount a disk you must be with root privileges. To connect/mount a disk to a catologe use:

$sudo mount /dev/sda /mnt

(what to mount, where to)

for avoiding “sudo” retyping use:

$sudo -i


You can choose either the devie you want to unmount or “from where” you want to disconect it

from where:

$umount /mnt/

or by name 

$umount /dev/sda






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