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Linux Command for System Administrator

Basic command for system monitoring

  1. sudo du -a / | sort -n -r | head -n 20 # list disk usage
  2. journalctl | grep "error" # log messages, kernel messages, and other system-related information
  3. dmesg --ctime | grep error # Show kernel ring buffer
  4. sudo journalctl -p 3 -xb # Check the lock file
  5. sudo systemctl --failed # Service that failed to load
  6. du -sh .config # File size of a specific directory
  7. find . -type f -exec grep -l "/dev/nvme0n1" {} + # find file and exce command with grep, {} is the output for each & +,\; is the terminator

Reset password (for forgotten password)

Reser Root

  1. init=/bin/bash # from grub commnad mode, find the kernel line containing linux then add at the end of linux command
  2. ctrl+x or F10 # to save the changes and boot
  3. mount -o remount,rw / # mount the root system for (r,w)
  4. passwd # change the password
  5. reboot -f # force reboot, after that you can boot with new passwd you set

Reser User

  1. rw init=/bin/bash # from grub commnad mode, find the kernel line containing linux then add at the end of linux command
  2. ctrl+x or F10 # to save the changes and boot
  3. passwd username # change the password
  4. reboot -f # force reboot, after that you can boot with new passwd you set

Some useful Command

  1. grep -Irl "akib" . # this will find file contain akib in the current dir
  2. grep -A 3 -B 3 "nvme" flake.nix # this will find nvme in flake.nix file with before and after with 3,3 line
  3. sed -i "s/akib/withNewText/g" file.txt # sed will changes the all occurance with new text in a file
  4. cat /etc/passwd | column -t -s ":" -N USERNAME,PW,UID,GUID,COMMENT,HOME,INTERPRETER -J -n passwdFile # will seperate passwd file based on ":" delemeter and show as column format then the "-J" flag will convert it into json file
  5. cat /etc/passwd | awk -F: 'BEGIN {printf "user\tPW\tUID\tGUID\tCOMMENT\tHOME\tINTERPRETER\n"} {printf "%s\t%s\t%s\t%s\t%s\t%s\t%s\n", $1, $2, $3, $4, $5, $6, $7}'
  6. cat /etc/passwd | column -t -s ":" -N USERNAME,PW,UID,GUID,COMMENT,HOME,INTERPRETER -H PW -O UID,USERNAME,GUID,COMMENT,HOME,INTERPRETER # "-H" remove specific column "-O" reorder column