Linux commands for sysadmins (but not only, part 1)

Whether you're a Linux or an OS/X user, you often ends up starting a terminal and typing some shell commands.

Following is a list of some commands I often use, and they're by no means exhaustive. They are given as examples, and a second list will include other topics like benchmarking, network, or performance. Some require the root password or at least be part of the sudoers.

Be warned these are mainly Linux commands, used from a Linux Mint 19.3 machine. My advice is to man each one (when available) to list all the numerous possibilities for a specific command. man is always your friend and you can often discover the missing parameter you need to solve your problem.

Dealing with hardware

• list your hardware configuration (the most comprehensive): inxi -Fxz

• disks

what?	command
list all hard disks	lsblk -o NAME,TYPE,SIZE,MODEL,SERIAL,VENDOR -d
get information on a disk	sudo hdparm -i /dev/sda
list partitions	sudo sfdisk -l /dev/sda
mounted disks	df -T -x squashfs -x tmpfs -x devtmpfs
sanitize or partition	dcfldd if=/dev/urandom od=/dev/sdX
copy a disk or partition to a file image	dcfldd if=/dev/sdX of=image.img hash=sha1 conv=sync,noerror
list usb devices	lsusb
list PCI devices	lspci

Files

Listing files with ls

list	command
sort by size (largest first)	ls -lS
sort by time (newest first)	ls -lt
reverse sorting order	add the -r flag
recursive	ls -lR
sort by extension	ls -lX

Using the tree command

If not installed: sudo apt-get install tree

list	command
only directories	tree -d
full path with files	tree /usr -f
on the current filesystem only	tree . -x
only subdirectories	tree . -L 1
only files with pattern	tree . -P ".jpg"*
without indentation (like find)	tree . -i -f
output as a JSON object	tree . -J
output as an XML object	tree . -X

Finding files

find is a very feature rich command and not easy to master at first. man find is your friend!

find	command
files matching a pattern	find . -name '.jpg'*
files matching a pattern (case insensitive)	find . -iname '.jpg'*
files only on current mounted filesystems	find . -mount -name ".jpg"*
owned by userID	find . -user 1000
whose permissions are 644	find . -perm 644
greater than 50M	find / -size +50M
modified more than 1 day	find . -mtime +1
only directories	find . -type d
only (regular) files	find . -type f
executable files	find . -executable -type f
using a regex	find . -regextype posix-extended -regex "(..jpg

Open files

lsof is a very powerful and versatile command.

find	command
open files for a list of users	lsof -u johndoe,1000
open files by a list of processes	lsof -p 1999,2050
on a specific fiessystem	lsof /dev/sdb1

Photo by Barn Images on Unsplash

Comments

[James McPherson]

I'd have started with saying that the man command is your friend, because it provides you with the manual pages for each of these commands. It's meta-powerful :-)

[Loki Le DEV]

Great and concise summary!
I would add find -delete option in the list.
Also for disk usage I discovered ncdu which a nice command line tool.