Helpful-Commands

Remove many/thousands of files

Sometimes the rm (Remove) command will not work when there are too many files in a folder or will take forever. You can use a for loop to remove the files in a folder. Just change your directory to the folder where you want to remove the files and run the below command. This will delete all files in the directory except folders

for i in * ; do rm $i ; done

Remove files older then x

Sometimes you only want to keep x iterations of files for example of zipped backups, so you need to remove all files older then x days. With the below command you can remove all files older then 5 days.

find /path/to/files/* -mtime +5 -exec rm {} \;

Search recursive through files with a pattern

Sometimes you need to find all files with a specific pattern, for example a domain or ip-address in a config. The -r option searche recursive, -n shows the line number for every finding and -w searches for whole words.

grep -rnw '/path/to/somewhere/' -e 'pattern'

Outbound NAT iptables

With the below command you can NAT your traffic from a routed network via a local interface, in this example all packets from a local network on LAN gets NATed through the wifi interface.

sudo iptables -t nat -A POSTROUTING -o wlp2s0 -j MASQUERADE

Set file permissions recursive for every file or folder in a path

Files

find /my/path -type f -exec chmod 0644 {} \;

Folder

find /my/path -type d -exec chmod 0755 {} \;

Convert text to base64

echo -n test | base64

Split large files to smaller ones

Sometimes you need to split a large file into a few smaller ones so you can upload them to systems with a file limitation. After that you can recreate the source file. Split large files

split -b 512M large.dat

Recreate the source file

cat large1.dat large2.dat > large.dat

Listen on a specific port with tshark

tshark -f "udp port 162" -i any

Create bootable linux USB key

sudo dd bs=4M if=/path/to/file.iso of=/dev/sdx status=progress oflag=sync

Show lldp neighbour

With the below command you can see to which switch or device you are connected on the LAN port.

sudo lldpcli show neighbors

Show all disks in AVAGO raid controller

storcli /c0 /eall /sall show

Create a zip with all files from a folder via cli

zip -r myfiles.zip mydir1 mydir2

Create WiFi QR-Code

qrencode -t png -o ~/filename.png 'WIFI:S:SSID-Name;T:WPA2;P:Password;;'

Clear systemd DNS cache

sudo resolvectl flush-caches 

or for older versions

sudo systemd-resolve --flush-cache

Show systemd DNS cache statistics

sudo systemd-resolve --statistics

Test disk performance with dd

The below command writes a 10GB file directory to disk without using RAM as cache.

dd if=/dev/zero of=/testfile bs=10G count=1 oflag=direct  

Show file permissions as number

stat -c "%a %n"  file.txt

Create one log file from many

All Logs

for i in * ; do echo $i; cat $i/logs/access_ssl_log >> /tmp/all_access.log ; done

Logs with pattern

for i in * ; do echo $i; grep "mykeyword" $i/logs/access_ssl_log >> /tmp/all_access.log ; done

List files by size

** Files and directories**

du -sh -- *  | sort -rh  # Files and directories, or

Directories only

du -sh -- */ | sort -rh  # Directories only

Mount qcow2 image

Mount

sudo guestmount -a /var/lib/libvirt/images/myimage.qcow2 -m /dev/sda1 --ro /mnt/tmp

Unmount

sudo guestunmount /mnt/tmp

Delete empty files in folder

find . -name '*.log' -size 0 -print0 | xargs -0 rm

Forever loop

while true; do echo something; done

Update dynamic nameserver entry from cli

nsupdate
server localhost
add myserver.local 3600 A 1.1.1.1
send

Show Output of all commands in Shell script

sh -x myscript.sh

Show and sort swap usage by process

for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done | sort -k 2 -n -r | less

fail2ban

Show status for jail

fail2ban-client status JAILNAME

Unban IP

fail2ban-client set JAILNAME unbanip ip

Ban IP

fail2ban-client set JAILNAME banip ip

convert iso to qcow2 image

qemu-img convert -O qcow2 file.iso file.qcow2