Linux commands

23.06.2022 — devops, scripting101 — 1 min read

tee : read from stdin and write to stdout as well as file(s)

df -h | tee disk_usage.txt

1Filesystem      Size  Used Avail Use% Mounted on
2dev             7.8G     0  7.8G   0% /dev
3run             7.9G  1.8M  7.9G   1% /run
4/dev/nvme0n1p3  212G  159G   43G  79% /
5tmpfs           7.9G  357M  7.5G   5% /dev/shm
6tmpfs           7.9G     0  7.9G   0% /sys/fs/cgroup
7tmpfs           7.9G   15M  7.9G   1% /tmp
8/dev/nvme0n1p1  511M  107M  405M  21% /boot
9/dev/sda1       459G  165G  271G  38% /data
10tmpfs           1.6G   16K  1.6G   1% /run/user/120

Ouput also saved to the disk_usage.txt file

awk : manipulate text data

The file contents could look something like this:

1fristName       lastName        age     city       ID
2
3Thomas          Shelby          30      Rio        400
4Omega           Night           45      Ontario    600
5Wood            Tinker          54      Lisbon     N/A
6Giorgos         Georgiou        35      London     300
7Timmy           Turner          32      Berlin     N/A

Print all

1awk '{print $0}' information.txt

Ouptut:

1fristName       lastName        age     city       ID
2
3Thomas          Shelby          30      Rio        400
4Omega           Night           45      Ontario    600
5Wood            Tinker          54      Lisbon     N/A
6Giorgos         Georgiou        35      London     300
7Timmy           Turner          32      Berlin     N/A

Print first column

1awk '{print $1}' information.txt

Ouput:

1Thomas
2Omega
3Wood
4Giorgos
5Timmy

Print line start with O (regex)

1awk '/^O/' information.txt

Output:

1Omega           Night           45      Ontario    600

head : print top N line from files

print lines between 10 and 20

1head -n 20 state.txt | tail -10

tail : print last N line from files

tail -f following logfile

less : showing part of file without loading entire file to memory, reduce using memory when accessing large text file

less -p "failure": start at first occurrence of pattern “failure” in the file.

less -N: show content with line number

touch : update modification time of file to current time, create file if not exist
cut: cutting out the sections from each line of files and writing the result to standard output
lsof: Listof Open Fileprovides a list of files that are opened

lsof -c Mysql : list all files opened by Mysql

lsof -u root : list all files opened by user root

lsof -u ^root : list all files opened by everyone except root

lsof -p PID : list all files opened by PID

ps: Process Status is used to list the currently running processes and their PIDs along with some other information depends on different options. It reads the process information from the virtual files in /proc file-system. /proc contains virtual files, this is the reason it’s referred as a virtual file system

ps -aux: view processes owned by a user named "x"

netstat: Network Statistic
&``disown``nohup :

& puts the job in the background, that is, makes it block on attempting to read input, and makes the shell not wait for its completion.

disown removes the process from the shell's job control, but it still leaves it connected to the terminal. One of the results is that the shell won't send it a SIGHUP. Obviously, it can only be applied to background jobs, because you cannot enter it when a foreground job is running.

nohup disconnects the process from the terminal, redirects its output to nohup.out and shields it from SIGHUP. One of the effects (the naming one) is that the process won't receive any sent SIGHUP. It is completely independent from job control and could in principle be used also for foreground jobs (although that's not very useful).