List of essential Debian/Ubuntu commands

File handling

ls

The ls command lists the files in a directory:

  • -l = details
  • -t = sort by modification date
  • -r = reverses the ranking order
  • -R = lists all subfolders and their files
  • -h = more readable size in M/G/T
  • -a = displays hidden files and folders
  • For convenience, please use ls -ltrh.

head displays the first lines of a file:

  • -n = number of lines to display

tail

The tail command displays the last lines of a file:

  • -n= number of lines to display
  • -f = allows to monitor the log (up to Ctrl + C)

Monitoring tools

  •  top -> The classing monitoring
  •  htop -> More advanced version
  •  iftop -> Network monitoring
  • iotop -> Monitoring of disk activity by process

Network

  • netstat-> Allows you to obtain a large amount of information

netstat -tupan argument provides most of the necessary information (e.g. open connections, listening ports)

Disk space

df

df allows you to list filesystems with occupied/free disk space:

  • -h = more readable size in M/G/T
  • -i = displays occupied/unoccupied inodes

du

du displays the disk space used by a tree:

  • -s = Means summary edition, it displays only the summary of the tree structure there ar no display of sub-folders
  • -k = display in KB
  • -m = display in MB
  • -h = display with the most readable unit
  • -d ou --max-depth = depth of the listing (e.g. "du -d 1" will display the compiled size of the 1st level sub-folders)

Miscellaneous

sort

sort allows you to sort the display:

  • -k = column used for sorting
  • -n = sort by number
  • -h = intelligent sorting by size (useful if used with du)

uniq

uniq  allows you to delete duplicate lines:

  • -c = duplicate counts

wc

wc counts the number of characters, words, lines:

  • -c = counts the characters
  • -l = counts the lines
  • -w = counts the words

Combined commands

  • netstat -tupan | grep LISTEN - lists the listening ports.
  • du -h -d 1 | sort -h - display of the size of the first level folders with sorting by size
  • tail -n 100000 access.log | awk '{ print $1; }' | sort | uniq -c | sort -k 1 -n - IPs ranking on the last 100 000 lines of the access.log file (e.g : 1st column of the file = IP address of the customer)
  • cat file.txt | uniq | wc -l - Displays the number of unique lines