Linux

TL;DR

cd / and run

sudo du -sh * --exclude proc --exclude sys --exclude dev

and then repeat for the largest directory shown (by cding to that directory and running the command above)

Long answer

If you get No space left on device errors on Linux, this means that one of your mounted disks has (virtually) no space left to write on.

First, check which device is the one that has no space left:

$ sudo df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            2.4G     0  2.4G   0% /dev
tmpfs           494M   51M  444M  11% /run
/dev/xvda1       46G   17G   11M 100% /
tmpfs           2.5G     0  2.5G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           2.5G     0  2.5G   0% /sys/fs/cgroup
tmpfs           494M     0  494M   0% /run/user/1003

Check the Use % column – you can see that the device mounted on / (your root filesystem, i.e. the one where your system is mounted) is full. In 95% of all cases it’s the root filesystem that’s full.

This post only covers the case where your root filesystem is full. In most other cases, it’s either /dev/shm (in which case rebooting your system typically works) or an external drive (in which case you have to figure out for yourself which directories can be deleted).

Probabilistic method:

This quick check tries to identify the most likely candidates first (based on admin experience). Run this in your shell:

sudo du -sh /var/lib/docker /var/lib/mysql /var/lib/postgresql /home/

This might take some time to complete.

Check if one of those directories is so large that it eats up a significant fraction of your drive space. If not, I recommend going forward with the Simple method:

Simple method:

Copy & paste this into your shell:

function findLargestSubdir { cd "$1" && sudo du -sb * --exclude proc --exclude sys --exclude dev | sort -n ; }

then run

findLargestSubdir /

This will tell you which directory is the largest. It might take a long time to compute the size of all directories. This command will only print anything once it’s finished! The numbers are in bytes.

The last element in the list is the largest one!

Now, run the same command inside the largest directory to find the largest sub-directory. For example, if /var happens to be the largest directory, run

findLargestSubdir /var

which will show you the largest directory in /var. Continue checking the largest subdir(s) using findLargestSubdir until you found out what ate up all the space on your disk.

Advanced method: Much quicker but more complex

If it takes more than 2 minutes to compute the size of all directories, I recommend following this interactive procedure as root (sudo):

1. ls -1 to show all files and directories in /. Example output:

   # ls -1 /
   bin
   boot
   dev
   etc
   home
   initrd.img
   initrd.img.old
   lib
   lib64
   lost+found
   media
   mnt
   opt
   proc
   root
   run
   sbin
   snap
   srv
   sys
   tmp
   usr
   var
   vmlinuz
   vmlinuz.old

2. Now run du -sh *. This will try to compute the size of each of those files and directories. Typically this command will stall for a long time when trying to compute the size of one directory (if that directory has a huge number of files in it). For example, when you see the output

   # du -sh *
   17M     bin
   157M    boot
   0       dev
   7.7M    etc

   and then nothing happens for more than 30 seconds, look up the next entry after the last entry in the list ( etc in this example) in the output of ls -1 above. In this example, this would be /home. Since du -sh took so long computing the size of /home it’s very likely (though not guaranteed) that /home is the directory that takes up so much space. Also check the number

3. In whatever directory you found to be a candidate for being the largest directory, run ls -1 <directory> again and check

Note that this method sometimes has a tendency to identify directories that recursively contain many files as opposed to directories whose total size is large. Therefore, you might need to go back in case you can’t identify any directories that eat up a large fraction of your hard drive space.

On Linux users often have the issue that normal users can’t access some USB devices while root can. Most pages on the internet try to address this issue individually for each device, but most users don’t need that granularity, they just want it to work.

This post provides a method 

Installation

Run this in your favourite shell:

wget https://techoverflow.net/scripts/udev-install-usbusers.sh | sudo bash -s $USER

This will print:

SUBSYSTEM=="usb", MODE="0666", GROUP="usbusers"
USB device configuration has been installed. Please log out and log back in or reboot

then log out and log back in (or close your SSH session and log back in).

In case this doesn’t work, reboot!

How it works

1. It creates a group called usbusers
2. It adds your user ($USER) to the usbusers group. You might need to sudo usermod -a -G usbusers $USER for additional users that should have access to USB devices!
3. Then it creates an udev config file /etc/udev/rules.d/99-usbusers.rules with the following content:

   SUBSYSTEM=="usb", MODE="0666", GROUP="usbusers"

4. It then tries to reload & trigger udev using udevadm. This usually means you don’t have to reboot

In effect, it sets the group to usbusers for every USB device, no matter what type and ensures the group has write access. This is why this solution is so generic – it’s not limited to a specific type of USB device.

If you want to convert my.pdf to my.svg, use eps2svg like this:

eps2svg my.eps

Even though the name eps2svg may suggest it can only read EPS files, the program will handle PDFs just fine!

This command produces my.svg – note that if my.svg already exists, eps2svg will create my_1.svg, my_2.svg and so on and will not overwrite my.svg!

You can also use this shell function:

function pdf2svg { eps2svg "${1%.*}.eps" "${1%.*}.svg" ; }

This will always produce my.svg, overwriting it if it already exists!

Usage example:

pdf2svg my.pdf # Produces my.svg

To temporarily disable syntax highlighting in GNU nano, use the -Ynone option:

Instead of

nano myfile.php

use

nano -Ynone myfile.php

In order to permanently disable nano syntax highlighting, run this command:

echo "alias nano='nano -Ynone'" >> ~/.$(echo $SHELL | rev | cut -d/ -f1 | rev)rc
source ~/.$(echo $SHELL | rev | cut -d/ -f1 | rev)rc # Reload immediately

This will add nano -Ynone as an alias for nano into your .bashrc or .zshrc

To get just the name of the shell, e.g. bash or zsh, use

echo $SHELL | rev | cut -d/ -f1 | rev

Example:

$ echo $SHELL | rev | cut -d/ -f1 | rev
bash

To get the full path of the current shell executable, use

echo $SHELL

Example:

$ echo $SHELL
/bin/zsh

Run

id -g

to get the GID of the current user’s primary group. Example:

$ id -g
1000

You can also get the GID of another user’s primary group:

$ id -g root
0

Run

id -u

to get the current user’s UID. Example:

$ id -u
1000

You can also get another user’s UID:

$ id -u root
0

If you see an error message like this in Wireshark:

this is because your current user doesn’t have permission to capture packets from your network card.

This can be the case even if you have selected to allow normal users to capture packets during the Wireshark installation process. This is because the setting only takes effect after logging out and logging back in (or rebooting).

To fix the issue temporarily without logging out, run Wireshark as root: sudo wireshark

In order to fix the issue permanently, ensure your user is added to the wireshark group:

sudo usermod -a -G wireshark $USER

and then log out and log back in again (or reboot your computer).

On the command line, run

sudo mokutil --sb-state​

This will tell you

SecureBoot enabled​_

if secure boot is currently active on your machine or

SecureBoot disabled

else.

In case you see an error message like

bash: command not found: mkoutil

you need to install mokutil first using

sudo apt install mokutil​_