*nix zone

Command line tools

Generate random passwords from command line

openssl rand -base64 10

openssl rand -hex 10

Remove <CR> characters from file (Mac OS X tested)

sed -i.bak $'s/\r//' file`

tmux usage

list – tmux ls

resume – tmux a

detach – Ctrl + b, press d

Copy all stdout and stderr to file

python3 very-verbose-program.py 2>&1 | tee -a results.log

Disk usage

Usage by directory

du -h -d 1 /

Overall stats

df -h

Find files and run some command per file

find postgres_data/base/ -regex '.*[0-9]+' -exec pg_filedump "{}" \; | grep Error | sort | uniq

find postgres_data/base/ -regex '.*[0-9]+' -print0 | xargs -0 -n1 pg_filedump | grep Error | sort | uniq

Find large files and directories

du -hs * | sort -rh | head -5

sudo find / -size +500000 -print

sudo find / -size +500000 -exec sudo ls -lah "{}" \;

sudo du -k /* | awk '$1 > 500000' | sort -nr

Create tmpfs partition

sudo mkdir /mnt/tmpfs
sudo chmod -R 777 /mnt/tmpfs
sudo mount -t tmpfs -o size=512m ext4 /mnt/tmpfs
sudo umount /mnt/tmpfs

Create virtual disk with limited storage

1. Create a file of the size you want (here 10MB)

   dd if=/dev/zero of=/home/username/test bs=1024 count=10000

2. Make a loopback device out of this file

   losetup -f /home/username/test

3. Format that device in the file system you want

   mkfs.ext4 /dev/loopXX

4. Mount it wherever you want (/mnt/test should exist)

   mount /dev/loopXX /mnt/test

Don’t forget to unmount and clean up loop device after use, with sudo losetup -d /dev/loopXX.

System stress/load tests

sudo apt install sysbench
sysbench --test=cpu --cpu-max-prime=20000 --num-threads=4 run

Run command and update its output every N_SECONDS

watch -n N_SECONDS <your command>

Manually generate a locale

localedef -i en_US -f UTF-8 en_US.UTF-8

Show number of threads per process

It also counts main process twice, so do -1 to the result.

ps -M 81581 | wc -l

Network

OpenVPN

sudo openvpn --config '/path/to/openvpn/config.ovpn'

To use with login/password create pass.txt with:

login
password

and add auth-user-pass /path/to/pass.txt to config.ovpn.

Wireshark

Filter packets by data size and value

data.len > 1 or (data.len == 1 and data in {Q K Z I P X B E C S D H c d f F n 2})

Change default TTL value of IP network packages

Maybe helpful to hack mobile hotspot limitations on some cellular data plans.

• Run sudo sysctl -w net.inet.ip.ttl=65
• Or make it persistent, put net.inet.ip.ttl=65 into /etc/sysctl.conf

WiFi info

nmcli dev wifi

sudo apt install wavemon
wavemon

Appearence

GNOME tweaks

sudo apt install gnome-tweak-tool