linux-pro-tips

When you had enough of troubleshooting

I. Specific DE/distro/hardware etc. problems:

1. GNOME
2. Arduino
3. Xfce

II. General:

1. Wake-on-LAN with NetworkManager
2. Tar cheat sheet & basic functionality
3. Automount a drive
4. Bash - Output song names from multiple folders to a file
5. Iptables

III. Notes:

1. Bold sections should be considered important.
2. This project was made to remind myself to never fix a working machine.
3. Pull Requests are welcome.
4. The commands/information found in this project are provided without any kind of warranty.
5. In case of redistribution, be sure to keep and respect the GPL-3.0 License.

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Wake-on-LAN with NetworkManager

From wiki.archlinux.org

NetworkManager provides Wake-on-LAN ethernet support. One way to enable Wake-on-LAN by magic packet is through nmcli.

First, search for the name of the wired connection:

nmcli con show

NAME    UUID                                  TYPE            DEVICE
wired1  612e300a-c047-4adb-91e2-12ea7bfe214e  802-3-ethernet  enp0s25

By following, one can view current status of Wake-on-LAN settings:

nmcli c show "wired1" | grep 802-3-ethernet.wake-on-lan

802-3-ethernet.wake-on-lan:             default
802-3-ethernet.wake-on-lan-password:    --

Enable Wake-on-LAN by magic packet on that connection:

nmcli c modify "wired1" 802-3-ethernet.wake-on-lan magic

Then reboot, possibly two times. To disable Wake-on-Lan, substitute magic with ignore.

The Wake-on-LAN settings can also be changed from the GUI using nm-connection-editor.

You can disable Wake-on-Lan for all connections permanently by adding a dedicated configuration file:

/etc/NetworkManager/conf.d/wake-on-lan.conf

[connection]
ethernet.wake-on-lan = ignore
wifi.wake-on-wlan = ignore

Enable WoL in TLP

When using TLP for suspend/hibernate, the WOL_DISABLE setting should be set to N in /etc/tlp.conf to allow resuming the computer with WoL.

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Tar cheat sheet & basic functionality

From haskaalo/tarcheatsheet and cheat.sh/tar

Compress a file or directory

tar -czvf name-of-archive.tar.gz /path/to/directory-or-file

• -c: Create an archive.
• -z: Compress the archive with gzip.
• -v: makes tar talk a lot. Verbose output shows you all the files being archived and much.
• -f: Allows you to specify the filename of the archive.

Extract an Archive

tar -xvzf name-of-archive.tar.gz

• f: this must be the last flag of the command, and the tar file must be immediately after. It tells tar the name and path of the compressed file.
• z: tells tar to decompress the archive using gzip
• x: tar can collect files or extract them. x does the latter.
• v: makes tar talk a lot. Verbose output shows you all the files being extracted.

Create a compressed archive, using archive suffix to determine the compression program

tar caf target.tar.xz file1 file2 file3

List the contents of a tar file

tar tvf source.tar

Create a .gz archive and exclude all jpg,gif,... from the tgz

tar czvf /path/to/foo.tgz --exclude=\*.{jpg,gif,png,wmv,flv,tar.gz,zip} /path/to/foo/

Extract a specific file without preserving the folder structure

tar xf source.tar source.tar/path/to/extract --strip-components=depth_to_strip

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Automount a drive

From techrepublic.com

Locate the partition to mount

The first thing to be done is to locate the partition you want to mount. In this case, we'll be working with an entire drive. To do so type:

sudo fdisk -l

The output will be similar to the following:

Disk /dev/nvme0n1: 465,76 GiB, 500107862016 bytes, 976773168 sectors
Disk model: KINGSTON SA2000M8500G                   
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 35121E42-842O-F912-8451-0BO08894A1D8

Device           Start       End   Sectors   Size Type
/dev/nvme0n1p1    4096   1052671   1048576   512M EFI System
/dev/nvme0n1p2 1052672 976768064 975715393 465,3G Linux filesystem


Disk /dev/sda: 1,82 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: WDC WD20EZRZ-00Z
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 31616826-A6D4-4688-8847-D800B1356D7A 

Device     Start        End    Sectors  Size Type
/dev/sda1   2048 3907028991 3907026944  1,8T Linux filesystem

In this case the disk I want to automount is WDC WD20EZRZ-00Z, located at /dev/sda.

Locate the UUID

Next we need to find the UUID (Universal Unique Identifier) of the drive. To do that, issue the command:

sudo blkid

/dev/nvme0n1p1: LABEL_FATBOOT="NO_LABEL" LABEL="NO_LABEL" UUID="0FBE-6148" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="e1aba8f4-65d5-4b45-8206-4d5a92e3c105"
/dev/nvme0n1p2: UUID="3BO08d83-0511-b00b-8bbb-fef71ed2xddd0" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="614e5ef3-8dec-144a-8543-742d5c824aad"
/dev/sda1: LABEL="2big" UUID="bb7LM404-a173-4358-996a-2ae010be123c" BLOCK_SIZE="4096" TYPE="ext4" PARTLABEL="2big" PARTUUID="2f52b4a6-66b4-4582-98b0-b1ff8f0b44f8"

In this case the UUID will be bb7LM404-a173-4358-996a-2ae010be123c.

Permissions and mount point

Before we add the entry to fstab, we must first create a mount point for the drive. The mount point is the directory where users will access the data on the drive (as they can't access /dev/sda itself). So let's create a directory called data:

sudo mkdir /data

You'll want to also change the group ownership of that directory, so that users can access it. For this, you might create a group called data and then add users to the new group. After you've done that, you could then change the ownership of the mountpoint. All this could be done with the commands:

sudo groupadd data
sudo usermod -aG data $USER
sudo chown -R :data /data

Editing fstab

Start by opening /etc/fstab in your favorite editor (e.g. sudo nano /etc/fstab or sudo vi /etc/fstab etc.)

At the bottom of that file, we'll add an entry that contains the information we've discovered. The entry will look like this:

UUID=bb7LM404-a173-4358-996a-2ae010be123c /data    auto nosuid,nodev,nofail,x-gvfs-show 0 0

Breaking that line down, we have:

• UUID=bb7LM404-a173-4358-996a-2ae010be123c - is the UUID of the drive. You don't have to use the UUID here. You could just use /dev/sdj, but it's always safer to use the UUID as that will never change (whereas the device name could).
• /data - is the mount point for the device.
• auto - automatically determine the file system
• nosuid - specifies that the filesystem cannot contain set userid files. This prevents root escalation and other security issues.
• nodev - specifies that the filesystem cannot contain special devices (to prevent access to random device hardware).
• nofail - removes the errorcheck.
• x-gvfs-show - show the mount option in the file manager. If this is on a GUI-less server, this option won't be necessary.
• 0 - determines which filesystems need to be dumped (0 is the default).
• 0 - determine the order in which filesystem checks are done at boot time (0 is the default).

Save and close the file.

Testing the entry

Before you reboot the machine, you need to test your new fstab entry. To do this, issue the command:

sudo mount -a

If you see no errors, the fstab entry is correct and you're safe to reboot. Congratulations, you've just created a proper fstab entry for your connected drive. Your drive will automatically mount every time the machine boots.

Bash - Output song names from multiple folders to a file

OC

Put the script below in your root music directory and it will output the name of the songs to albums.txt.

Notes:

If your music does not correspond to the following pattern you can edit the regex in the script (now it's grep -E '[0-9][0-9]'):
NR Name eg. 06 Lose Yourself to Dance.flac or 08. Waltz for Zizi.flac etc.

Also if you have mp3, wav etc. files you can edit sed 's/.flac//g' to the respective file type (or make an OR operation for multiple types).

There are also two versions for Losslessclub, one for normal albums, web albums, vinyl rips etc. and one for discgraphy, which also includes the duration of the album (you have to edit this manually). If you don't know what I just talked about don't worry. Anyways, you can find them in this Gist.

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touch albums.sh && chmod +x albumes.sh and edit the file with your preffered editor.

#!/bin/bash

# Forbid root rights
[ "$EUID" == "0" ] && echo -e "\e[91mDon't use sudo or root user to execute these scripts!\e[0m" && exit

export ALBUME="$PWD/albums.txt"

: > "$ALBUME" # clear (and create) file

for dir in ./*/
do cd -P "$dir" || continue
   printf %s\\n "$PWD" >&2
   echo -e "${PWD##*/}\n" >> "$ALBUME" && \ls -lha | cut -d " " -f 12-99 | grep -E '[0-9][0-9]' | sed 's/.flac//g' >> "$ALBUME" && echo -e "\n" >> "$ALBUME" && cd "$OLDPWD" || 
! break; done || ! cd - >&2

echo

(NOT RECOMMENDED):
You can also curl https://gist.githubusercontent.com/sabinM1/86a06a0785b01842aa316f68ed22f779/raw/albums.sh | bash in your root music directory (assuming you have curl installed) if you don't want to create a script file and you trust GitHub and me enough to run unverified scripts on your machine. The Gist is public and hopefully the same as the script above, but because there is a "hopefully", you never know what it's being transmitted to bash if you don't verify it.

Iptables

From thomas-krenn.com

Allow a port

Change tcp to udp if you need UDP.

sudo iptables -I INPUT -p tcp --dport PORT_NUMBER_HERE -j ACCEPT

Permanently save Iptables

You need to have the iptables-persistent package installed (apt install iptables-persistent).

On debian-based distro, run as root:

• IPv4:

iptables-save > /etc/iptables/rules.v4

• IPv6:

ip6tables-save > /etc/iptables/rules.v6

Restore Iptables from file

On debian-based distro, as root:

iptables-restore < /etc/iptables/rules.v4