Stefan Hornburg (Racke)

Linux Utils Cheatsheet

    Finding files with find

      Remove files by modification date

      Move old files to another directory

      Find files by permission

      Find large files

    Use ncdu

      Scan all files

    Use cat

      Show file contents

      Show whitespace

    Use tail

    Use sed

      Remove lines from output

      Extract lines

    Sort lines with sort

    Using date

      Epoch

    Using rsync

      Copy files instead of symlinks

      Sync only files with a certain extension from one directory tree to another

    Using ip

      Show network interfaces

      Add IP address

       IPv6

    Using lsof

      Open files

      Network connections

      See also

    Using ncat

    Using lftp

      Mirroring

      SSL

    Using curl

    Using wget

    Using convert

      Reduce file size of a JPG image

      Rotate image clockwise

      Combine images into a PDF file

      Convert SVG file to PNG with transparency

    Using pdfjam

    Using pdfScale

    Using zip

      Create password protected archive

    Using timeout

    Encryption with GnuPG

      Environment variables

        GNUPGHOME

Finding files with find

Remove files by modification date

This example shows how to remove all files with a modification date before 2016: 

find -type f -not -newermt 20160101 | xargs rm

Move old files to another directory

This example shows how to move a large number of files to another directory: 


find /var/www/userpics -name '*.jpg' -mtime +31 -print0 | xargs --null mv --target-directory=/backup/oldpics/

Find files by permission

Exact permission (read,write,execute for owner only): 

find -perm 700

Find large files

$ du -sh -t 20M $(find /tmp/ -type f)
30M    /tmp/OF0dXjBgX3/0207.zip
56M    /tmp/lYZNO1PD09/0703.zip
29M    /tmp/aF_jPhgvwD/0307.zip

Use ncdu

ncdu: NCurses Disk Usage

Scan all files

$ ncdu /

Use cat

Show file contents

$ cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 11 (bullseye)"
NAME="Debian GNU/Linux"
VERSION_ID="11"
VERSION="11 (bullseye)"
VERSION_CODENAME=bullseye
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

This file should be present on any modern Linux distribution.

Show whitespace

$ cat -vet

Use tail

Show file content without the first line: 

$ tail -n +2 test.csv

Use sed

Remove lines from output

Remove single line: 

$ sed '1d' file

Remove range of lines: 

$ sed '1,5d' file

Extract lines

Extract a single line for a file: 

$ sed '123q;d' file

The q stops processing the file when the line is reached.

If you want to see a couple of lines from a CSV alongside with the header: 

$ sed -n -e '1p' -e '809,820p' my.csv

Sort lines with sort

Sort by a column: 

~# sort -k 1 myfile

Sort numeric: 

~# sort -n myfile

Sort reverse: 

~# sort -r myfile

Using date

Display date a month ago: 

~# date -d "-1 month" +%Y-%m-%d

It automatically adjusts the day if the resulting date would be invalid.

Set time: 

~# date +%T -s "12:12:00"

Epoch

Display epoch 

$ date +"%s"
1626247585

Convert epoch to a date 

$ date -d @1626247585
Wed 14 Jul 09:26:25 CEST 2021

Using rsync

Copy files instead of symlinks

rsync -L /etc/letsencrypt/live/wildcard.linuxia.de/*.pem root@extern.linuxia.de:/etc/letsencrypt/live/wildcard.linuxia.de/.

Sync only files with a certain extension from one directory tree to another

rsync -av --include="*/" --include='*.status' --exclude='*' /samba/. .

Using ip

Show network interfaces

$ ip -a

Add IP address

$ sudo ip a add 192.168.36.11/24 dev eth0

IPv6

Show global reachable addresses: 

$ ip -6 addr show scope global

Using lsof

Open files

Show open files in a directory: 

$ lsof /mnt/backup
...

Network connections

$ lsof -i :80
COMMAND    PID     USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
nginx   431729     root    6u  IPv4 7170923      0t0  TCP *:http (LISTEN)
nginx   431729     root    7u  IPv6 7170924      0t0  TCP *:http (LISTEN)
nginx   431730 www-data    6u  IPv4 7170923      0t0  TCP *:http (LISTEN)
nginx   431730 www-data    7u  IPv6 7170924      0t0  TCP *:http (LISTEN)

It works with service as well, e.g. lsof -i:ntp.

See also

An lsof Primer

Using ncat

Retrieve CheckMK agent output: 

$ ncat agent.example.org 6556 < /dev/null

Using lftp

Mirroring

Mirror from remote FTP server to local server 

mirror -c source target

Please note that doesn't mirror dot files like .htaccess. To include these, adjust the default listing options: 

set ftp:list-options -a

SSL

In case you really need to disable SSL (not recommended), use the following command: 

set ftp:ssl-allow false

Using curl

Display the headers: 

$ curl --head https://example.org

Skip certificate check: 

# Shortcut: -k
$ curl --insecure https://example.org

Connect without DNS: 

$ curl https://example.org --connect-to example.org:93.184.216.34

Using wget

Display the headers: 

$ wget --server-response https://example.org

Using convert

Reduce file size of a JPG image

$ convert photo-large.jpg -quality 82 photo-small.jpg

Rotate image clockwise

$ convert image.jpg -rotate 90 image2.jpg

Combine images into a PDF file

$ convert 20220518_1450*.jpg photos.pdf

Convert SVG file to PNG with transparency

$ convert -background none image.svg image.png

Using pdfjam

Produce PDF from image and convert to A4 format: 

$ convert image.jpg image.pdf
$ pdfjam --paper a4paper --outfile image-a4.pdf image.pdf

Using pdfScale

Scale Ebay shipping label: 

$ pdfScale.sh -v -r a4 --hor-align left --vert-align top -s 'eBay label 26-12806-75319_250314_124842.pdf'

Homepage: https://github.com/tavinus/pdfScale

Using zip

Create password protected archive

$ zip -e sccl2.zip sccl2_2.9-4_all.deb sccl2-2.9-4.noarch.rpm
Enter password:
Verify password:
  adding: sccl2_2.9-4_all.deb (deflated 0%)
  adding: sccl2-2.9-4.noarch.rpm (deflated 26%)

Using timeout

Run dhclient with a time limit: 

$ timeout 10 dhclient -6

Encryption with GnuPG

Environment variables

GNUPGHOME

Select alternative home directory for GPG configuration and keys: 

   export GNUPGHOME=~/.gnupg-old/