Commands Line Utilities

Format Output

• Prints only unique line.

<command> | uniq

• Sorts the lines.

<command> | sort

• For making a structured table out of text and filter our specific info.

sudo docker images | awk -F ' ' 'NR==, NR==12 {print $3, NR-1}'

- sudo docker images => Prints the current docker images in the system.

- -F ' ' => Field separation is set to space.

- NR==2 => Start from row 2.

- NR==12 => End at row 12

- {print $3, NR-1} => The command to be executed, Here, print third column based on the field separator and print the line number.

Process

• Find PID of a known program.

pidof <application name>

• Find all the direct and indirect child processes of a process.

pstree -p <PID>

• List all the files opened by a process with PID.

lsof -p <PID>

• Find details of a file descriptor corresponding to a PID.

lsof -p <PID> -a -d <FD>

- -a => Stands for 'AND' Operation.

- -d => File descriptor for which we need to find details.

• Find Parent (PPID) of a process with PID.

File System

• Check filesystem type.

df -T <Path>

• See details about a mount.

findmnt -T <Path>

ps -o ppid= -o comm= -p <PID>

Host Command

pristal@personal-system:~$ host google.com
google.com has address 142.250.196.14
google.com has IPv6 address 2404:6800:4007:829::200e
google.com mail is handled by 10 smtp.google.com.
pristal@personal-system:~$ 

• To get the nameservers associated with a domain,

pristal@personal-system:~$ host -t ns google.com
google.com name server ns2.google.com.
google.com name server ns1.google.com.
google.com name server ns3.google.com.
google.com name server ns4.google.com.
pristal@personal-system:~$ 

• To get the mailserver associated with a domain,

pristal@personal-system:~$ host -t mx google.com
google.com mail is handled by 10 smtp.google.com.
pristal@personal-system:~$ 

- Mail server is smtp.google.com

- Here the priority is set to 10

NetCat Command

• nc

Dig Command

• dig