Useful Linux Commands
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This is my collection of useful Linux shell commands from the perspective of a developer who is not primarily a sysadmin, yet uses Linux on a daily basis to test and deploy code in local, staging, and production environments.
Many of these are curated from the amazing Server for hackers course.
SSH Commands
Generate an SSH key
ssh-keygen -t rsa -C "user@example.com" -b 4096
# optionally add a passphrase
Add an SSH key to your keychain (Mac)
Add a key to the keychain.
ssh-add -K ~/.ssh/id_rsa
# enter passphrase
List all the keys in your keychain.
ssh-keygen -l
Copy text to the clipboard
Mac
pbcopy < ~/.ssh/id_rsa.pub
# or
cat ~/.ssh/id_rsa.pub | pbcopy
Ubuntu
cat ~/.ssh/id_rsa.pub | /dev/clipboard
lsb_release
Shows info about the Linux distribution.
lsb_release -a
```
**Sample Output**
```bash
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.2 LTS
Release: 18.04
Codename: bionic
uname
Shows system info.
uname -a
Sample Output
Linux thebolapp-staging 4.15.0-1035-aws #37-Ubuntu SMP Mon Mar 18 16:15:14 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
uname -r
Sample Output
4.15.0-1035-aws
uname -i
x86_64
df -h
Shows file system disk space (-h for human-readable file sizes).
df -h
Sample Output
Filesystem Size Used Avail Use% Mounted on
udev 985M 0 985M 0% /dev
tmpfs 200M 816K 199M 1% /run
/dev/xvda1 20G 6.9G 13G 36% /
tmpfs 996M 0 996M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 996M 0 996M 0% /sys/fs/cgroup
/dev/loop0 18M 18M 0 100% /snap/amazon-ssm-agent/1068
/dev/loop2 90M 90M 0 100% /snap/core/6673
/dev/loop3 18M 18M 0 100% /snap/amazon-ssm-agent/930
/dev/loop5 92M 92M 0 100% /snap/core/6531
/dev/loop6 90M 90M 0 100% /snap/core/6818
/dev/loop1 18M 18M 0 100% /snap/amazon-ssm-agent/1335
tmpfs 200M 0 200M 0% /run/user/1001
du storage/ -cah -d 1 -t 20M | sort -hr
Disk usage. Useful to check how much space a directory, its subdirectories, and files, occupy. These are just some of the most useful flags and options that I use.
storage/check inside the specified directory (by default will check the current root)-cshows a summary of the total-ashows files in addition to directories-hhuman readable format-d 1looks 1 directory deep-t 50Mshows only files/directories over the specified size| sort -hrsort by size (-hsorts by human-readable sizes) (-rsorts in descending order of size)
Examples
Show the size of all 1st level subdirectories.
du -h -d 1
181M ./vendor
972K ./resources
112K ./config
113M ./storage
116K ./tests
728K ./app
148K ./database
36K ./routes
26M ./.git
40K ./bootstrap
9.0M ./public
331M .
Show the size of all 1st level subdirectories and files.
du -ah -d 1
181M ./vendor
368K ./composer.lock
4.0K ./.env
972K ./resources
4.0K ./.gitignore
112K ./config
113M ./storage
324K ./yarn.lock
4.0K ./server.php
20K ./README.md
4.0K ./composer.json
4.0K ./artisan
116K ./tests
728K ./app
4.0K ./.gitattributes
148K ./database
4.0K ./webpack.mix.js
4.0K ./phpunit.xml
4.0K ./.env.example
36K ./routes
32K ./tailwind.js
26M ./.git
4.0K ./.editorconfig
40K ./bootstrap
9.0M ./public
4.0K ./phpunit-printer.yml
4.0K ./package.json
331M .
Show the size of all 1st level subdirectories inside the storage/ folder.
du storage/ -cah -d 1
4.0K storage/oauth-public.key
3.2M storage/framework
110M storage/app
260K storage/logs
4.0K storage/oauth-private.key
113M storage/
113M total
Show the size of all 1st level subdirectories, with a summary of the total, sorted by size.
du -ch -d 1 | sort -h
36K ./routes
40K ./bootstrap
112K ./config
116K ./tests
148K ./database
728K ./app
972K ./resources
9.0M ./public
26M ./.git
113M ./storage
181M ./vendor
331M .
331M total
Show the size of all 1st level subdirectories that are larger than 20M, with a summary of the total, sorted by descending size.
du -ch -d 1 -t 20M | sort -hr
331M total
331M .
181M ./vendor
113M ./storage
26M ./.git
free
Shows memory + swap usage.
free -h
Sample Output
total used free shared buff/cache available
Mem: 1.9G 704M 361M 17M 925M 1.1G
Swap: 1.0G 39M 984M
ps
Shows currently running processes.
ps -aux
Sample Output
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.4 225480 9072 ? Ss Apr09 1:35 /sbin/init
root 2 0.0 0.0 0 0 ? S Apr09 0:00 [kthreadd]
root 4 0.0 0.0 0 0 ? I< Apr09 0:00 [kworker/0:0H]
root 6 0.0 0.0 0 0 ? I< Apr09 0:00 [mm_percpu_wq]
root 7 0.0 0.0 0 0 ? S Apr09 3:18 [ksoftirqd/0]
root 8 0.0 0.0 0 0 ? I Apr09 9:29 [rcu_sched]
root 9 0.0 0.0 0 0 ? I Apr09 0:00 [rcu_bh]
root 10 0.0 0.0 0 0 ? S Apr09 0:00 [migration/0]
...
To sort by descending memory usage ps aux --sort -rss.
As above but get first n lines ps aux --sort -rss | head -n15.
chmod
Change user, group, other permissions.
chmod u=rwx,g=rx,o=-rwx .ssh
# equivalent to
chmod u+rwx,g+rx,o-rwx .ssh
More advanced example:
chmod u-rw+x,g-rw+x,o-r+wx XXX
# output
---x--x-wx 1 forge forge 0 May 17 19:14 XXX*