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

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