Linux Commands Useful

Chmod

8
1
0: No permission
2
1: Execute
3
2: Write
4
3: Write and execute
5
4: Read
6
5: Read and execute
7
6: Read and write
8
7: Read, write, and execute

3
1
The owner can read, write, and execute the file.
2
The group can read, write, and execute the file.
3
Anyone else can read, write, and execute the file.

1
1
sudo chmod 660 /shome/file

Make folder write/read for all users

1
1
sudo chmod -R a+wr /some/folder

Make SH file executable

1
1
sudo chmod +x /some/folder

Delete old files

older than 30 days

2
1
find /opt/backup -type f -mtime +30 -delete 
2
find /var/log -name "*.log" -type f -mtime +30 -delete 

List files in directory

3
1
ls -ltr /path/dir
2
ls -ltr /path/dir | grep "filter-text"
3
ls -a # shows also hidden files

https://www.tecmint.com/sort-ls-output-by-last-modified-date-and-time/

Count files

3
1
cd ~/documents/api_asya_ai/requests_files/unprocessed
2
ls | wc -l#
3

List File systems

Available HDDs

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1
1
sudo fdisk -l

Disk UUIDs

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1
1
sudo lsblk -f 

Mounting disk

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1
1
sudo mount /dev/sdX /media/hdd

Automatic mounting

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7
1
sudo vim /etc/fstab
2

3
LABEL=cloudimg-rootfs   /        ext4   defaults        0 1
4
LABEL=UEFI      /boot/efi       vfat    umask=0077      0 1
5

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UUID="69d4002e-a45a-483e-a13b-a3a1ffb255fb" /media/hdd1 ext4 defaults,noatime,_netdev 0 2
7
/swapfile swap swap defaults 0 0

Mount points to these HDDs

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1
1
cat /proc/mounts

List current directory

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1
1
pwd

Find file

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2
1
find /dir -name "*Something*
2
  find /dir -iname "*Something*

https://www.geeksforgeeks.org/find-command-in-linux-with-examples/

Find text in files

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1
1
grep -i -A 5 -B 5 "string" FILE_PATTERN

https://www.thegeekstuff.com/2009/03/15-practical-unix-grep-command-examples/

Kill process

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2
1
kill -9 PROCES_ID
2
kill -9 $(ps aux | grep 'SOME TEXT IN PROCESS' | awk '{print $2}')

Zip a folder

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2
1
zip -r <output_file> <folder_1>
2
unzip <zip_file>

Find location of some app in global path

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1
1
whereis app_name

Symlinks

Create

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1
1
ln -s /path/source/folder_or_file /path/destination

Will result in /path/destination/folder_or_file

Find source

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2
1
readlink -f /path/to/syslink
2
readlink -f which command

Move betwween folders:

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3
1
cd..   (move directory up)
2
cd-    (move to previous directory)
3
cd ...(exact path)...   (move to some concrete folder)

Debug incoming requests HTTP netcat

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1
1
nc -l PORT

Test if port is accepting something

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1
1
netstat -a | grep PORT

Opening firewall ports

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1
sudo apt install firewalld firewall-config
2
sudo firewall-cmd --zone=public --add-port=5432/tcp --permanent 
3
sudo firewall-cmd --reload
4
sudo ufw allow 5432
5

6

7
sudo firewall-cmd --zone=public --add-port=80/tcp --permanent 
8
sudo firewall-cmd --reload

Recover non-bootable linux using HDD

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1
grep -i -A 5 -B 5 "error" ./var/log/dmesg
2
sudo tail ./var/log/syslog
3
sudo tail ./var/log/kern.log
4

5
grep -i -A 5 -B 5 "error" ./var/log/kern.log
6

7
cat ./etc/ssh/sshd_config
8

9
cat ./etc/iptables/rules.v4
10
sudo cat ./etc/ufw/user.rules
11
sudo rm -rf ./etc/firewalld/zones/

HPC:

Started tasks:

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2
1
showq -r
2
qstat

Videocard memory usage:

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4
1
ssh wn56   (choose wn... from showq -r)
2
logout   (iziet no wn)
3
watch nvidia-smi   (ctrl+C lai izietu)
4
htop

Starting/killing tasks:

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2
1
qsub -N reinis_freibergs -A ditf_ldi start_hpc.sh   (Example for start)
2
qdel ...(task name from qstat)...   (Kill a task)

Screens:

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3
1
screen -ls     (List all of the screen sessions for a user)
2
screen -rd ...(name of screen to log into)...
3
screen -S ...(new screen name)...

Console management:

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2
1
Ctrl+A D   (exit screen, program will continue to  run)
2
Ctrl+A K   (kill a screen)

Installing lates NodeJS

https://github.com/nodesource/distributions#debinstall

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2
1
curl -fsSL https://deb.nodesource.com/setup_19.x | sudo -E bash - &&\
2
sudo apt-get install -y nodejs

Append files through command line

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2
1
echo "user_allow_other" | sudo tee -a /etc/fuse.conf
2

Set hostname

Set and store

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1
1
sudo hostnamectl set-hostname www.something.com

Stored here

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1
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vim /etc/hostname