Category Archives: Too Good To

In this episode:

urlwatch for new daily Ubuntu Server ISO
systemd-run ephemeral timers as replacement for at
Mozillateam Firefox on Debian
systemd service: ExecStartPre as root
gdm3 autosuspend/shutdown behaviour

urlwatch for new daily Ubuntu Server ISO

Somewhat desparate because at the time of starting this post, the (pre-beta, non-LTS, not blaming anyone) server image in question was badly broken.

---
name: Ubuntu Server Daily ISO
url: https://cdimage.ubuntu.com/ubuntu-server/daily-live/current/SHA256SUMS
filter:
  - grep: .*-live-server-amd64.iso
---

systemd-run ephemeral timers as replacement for at

Goes great with “hardened” systems that deny use of at(1).

Run a command 60 seconds from now, via the user’s private systemd (after logout only if session lingering is enabled).

systemd-run --user --on-active=60s -- logger --tag foo "Hello world"

Run a command 2 minutes from now, privileged or as a specific user via the global systemd:

sudo systemd-run --uid="${LOGNAME}" --on-active=2m -- touch /tmp/hello

Insights

systemctl --user list-timers
journalctl --user -u 'run-*.timer'
sudo systemctl list-timers
sudo journalctl -u 'run-*.timer'

Mozillateam Firefox on Debian

$ sudo tee /etc/apt/sources.list.d/mozillateam-ppa.list <<Here
deb https://ppa.launchpadcontent.net/mozillateam/ppa/ubuntu jammy main
deb-src https://ppa.launchpadcontent.net/mozillateam/ppa/ubuntu jammy main
Here

$ sudo tee /etc/apt/trusted.gpg.d/mozillateam.asc < <(curl 'https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x0ab215679c571d1c8325275b9bdb3d89ce49ec21')

systemd service: ExecStartPre as root

[Service]
...
User=nonroot
Group=nonroot
ExecStartPre=+install -d /var/lib/theservice -o nonroot -g nonroot
ExecStart=/usr/sbin/theservice

See systemd.service, “special executable prefixes”.

gdm3 autosuspend/shutdown behaviour

Debian:

$ sudo apt-get install dbus-x11
$ sudo chsh -s /bin/bash Debian-gdm
$ sudo -i -u Debian-gdm
$ gsettings get org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type
'suspend'
$ dbus-launch gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type nothing
$ gsettings get org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type
$ exit
$ sudo chsh -s /bin/false Debian-gdm

Arch/Garuda:

$ sudo chsh -s /bin/bash gdm
$ gsettings get org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type
'suspend'
$ dbus-launch gsettings set org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type nothing
$ gsettings get org.gnome.settings-daemon.plugins.power sleep-inactive-ac-type
$ exit
$ sudo chsh -s /usr/bin/nologin gdm

Too Good To, UNIX & Linux

Too good to #0008

7. March 2023 #!/bin/blog

rinetd-style circuit level gateway in systemd

This accepts port 465/tcp and forwards all connections to a service running somewhere else on 1194/tcp.

The socket unit accepts the connection on port 465:

# /etc/systemd/system/tcp465-to-tcp1194.socket
[Unit]
Description="openvpn 465/tcp to 1194/tcp (socket)"

[Socket]
ListenStream=465

[Install]
WantedBy=sockets.target

systemd-socket-proxyd connects to the backend:

# /etc/systemd/system/tcp465-to-tcp1194.service
[Unit]
Description="openvpn 465/tcp to 1194/tcp (service)"

[Service]
ExecStart=/lib/systemd/systemd-socket-proxyd 10.12.13.14:1194
User=proxy

(Anyone old enough to remember that this was called a plug-gateway in the TIS Firewall Toolkit?)

Python pip/virtualenv/pipenv micro-HOWTO

Clone project with wacky dependencies:

git clone https://github.com/example/project.git

Install dependencies (from requirements.txt):

pipenv install (-r requirements.txt)

Run:

pipenv run ./script

Template for git commit message

Create the template, I prefer it outside the repository:

(blank line)
(blank line)
foo#1234 is the neverending story I'm constantly working on

Configure the path, relative to the repository root:

git config commit.template ../commit-template-for-foo.txt

python, Too Good To, UNIX & Linux

Too good to #0007

1. February 2023 #!/bin/blog

Disable the dynamic motd on Ubuntu and everywhere else

This is without messing around in /etc/pam.d or doing things that may be reverted by future updates. Remember to systemctl enable disable-dynamic-motd.timer.

# /etc/systemd/system/disable-dynamic-motd.timer
[Unit]
Description=Disable all the dynamic-motd scriptlets (timer)

[Timer]
OnBootSec=10
OnActiveSec=3600

[Install]
WantedBy=timers.target

# /etc/systemd/system/disable-dynamic-motd.service
[Unit]
Description=Disable all the dynamic-motd scriptlets (service)

[Service]
Type=oneshot
ExecStart=sh -c 'chmod -v -x /etc/update-motd.d/*'

Disable verbose logging on realmd.service

Problem on AD-member Linux client, realmd logs thousands of redundant messages:

Feb 01 11:11:34 kvm-28ca realmd[22302]: client using service: :1.1042
Feb 01 11:11:34 kvm-28ca realmd[22302]: holding daemon: :1.1042
Feb 01 11:11:34 kvm-28ca realmd[22302]: client gone away: :1.1042
Feb 01 11:11:34 kvm-28ca realmd[22302]: released daemon: :1.1042

Solution, disable debug logging in the systemd unit by introducing this drop-in:

# /etc/systemd/system/realmd.service.d/override.conf
[Service]
LogLevelMax=info

Sorting Debian package versions

dpkg –compare-versions is not exactly a secret, but I’ve wrapped a script around it to visualize and better wrap my head around non-straightforward naming schemes:

$ cat test.txt
2.1
2.2~pre01
1.0
2022-01.1~pre03
2.1-bugfix-foo
2.1~bugfix-foo
2.2
2022-01~foo~bar
2022-01
1.0
0
3
2022-01~foo

$ ./dpkg-sort-versions < test.txt
Sorted from lowest (oldest) to highest (latest):
0
1.0
1.0
2.1~bugfix-foo
2.1
2.1-bugfix-foo
2.2~pre01
2.2
3
2022-01~foo~bar
2022-01~foo
2022-01
2022-01.1~pre03

Script is here.

Too Good To, UNIX & Linux

Too good to #0006

20. November 2022 #!/bin/blog 1 Comment

“Sudo on demand” from TGT0003 considered more useful for downgrading privileges on the fly

#!/usr/bin/env bash

want_user=letsencrypt
am_user="$(id -un)"
printf "Running as: %s\n" "${am_user}"
if [[ "${want_user}" != "${am_user}" ]]
then
        printf "Re-executing with sudo.\n"
        exec sudo -u "${want_user}" "${0}"
fi
...

JSON export of all installed packages on Debian/Ubuntu

#!/bin/bash

function dpkg_json(){
    printf "{\n"
    format='"${Package}": { "Version": "${Version}", "Architecture": "${Architecture}", "Status": "${db:Status-Abbrev}" },\n'
    dpkg-query --show --showformat="${format}" | sed '$s/,$//'
    printf "}\n"
}

dpkg_json | jq .

Urlwatch for a new version of a package in the Ubuntu package pool

---
name: "Ubuntu Curtin package (waiting for apt-key fix)"
url: http://archive.ubuntu.com/ubuntu/pool/main/c/curtin/
filter:
  - xpath: //table//td[2]
  - html2text
  - grep: ^curtin.*\.deb$
---

Too Good To, UNIX & Linux

Too good to #0005

1. November 2022 #!/bin/blog

Prioritizing own NTP servers for systemd-timesyncd

# cat /etc/systemd/timesyncd.conf.d/timesyncd-corporate.conf 
[Time]
NTP=ntp1.example.com ntp2.example.com ntp.ubuntu.com

Test if text is empty (even if it does contain a linebreak)

Good job by: https://unix.stackexchange.com/q/386499/2028

if ! grep -q '[^[:space:]]' "${file}"; then echo "Text is empty"; fi

Watch for changes in the Gnome registry

(To reproduce manual changes, for configuration management.)

dconf watch / # (Sorry, thats all)

Trigger Debian/Ubuntu unattended-upgrade

(For testing configuration changes)

rm /var/lib/apt/periodic/*
systemctl start apt-daily.service 
systemctl start apt-daily-upgrade.service

And remember:

tail -f /var/log/unattended-upgrades/*log

Too Good To, UNIX & Linux

Too good to #0004

7. October 2022 #!/bin/blog 1 Comment

systemd, the good parts: monotonic timers

When systemd makes you suffer because “run job every 10 minutes” is infinitely harder to specify than in crontab, remember there are monotonic timers in systemd that aren’t derived from wallclock time, or “Calendar Events” as they call it.

Run timer once 60 seconds after system startup, then every 10 minutes after the job finished:

# /etc/systemd/system/demo.timer
[Unit]
Description=demo monotonic timer

[Timer]
OnStartupSec=60
OnUnitInactiveSec=600

[Install]
WantedBy=timers.target    # When in a system session
# WantedBy=default.target # When in a user session (~/.config/systemd, systemctl --user etc.)

Python: Use tabulate to format output in columns

#!/usr/bin/env python3
from tabulate import tabulate

data = [
	[ 'foo', 'bar', 'baz' ],
	[ 'spam', 'eggs', 'bacon' ]
]

headers = ['Eine', '2', 'Whatever']

print(tabulate(data, headers=headers, tablefmt='simple'))

Output:

$ ./tab.py 
Eine    2     Whatever
------  ----  ----------
foo     bar   baz
spam    eggs  bacon

virsh/libvirt, automate key presses

(* Updated to sleep 5 seconds after each keypress.)

for key in R E I S U B; do virsh send-key "${domain}" KEY_LEFTALT KEY_SYSRQ KEY_${key}; sleep 5; done

Too Good To, UNIX & Linux

Too good to #0003

22. September 2022 #!/bin/blog

Linux uptime in seconds, once and for all

awk '{printf "%i\n", $1}' /proc/uptime

“Sudo on demand”, re-exec shell script with sudo if not running as root

#!/usr/bin/env bash
printf "Running as: %s\n" "$(id -un)"
[[ ${EUID} -ne 0 ]] && printf "Re-executing with sudo.\n" && exec sudo "${0}"

See also TGT0006, this is just as useful for downgrading privileges on the fly.

“When was the last time apt-get on that Debian/Ubuntu machine installed package upgrades?”

Reliably answering this is a lot harder than it looks, subject of countless discussions and really does need to parse /var/log/apt/history.log, which is painful.
The script below maintains a file /var/log/apt/lastupgrade with the last upgrade’s time stamp, for further processing.
Does NOT track invocations of apt-get upgrade that did not lead to package upgrades.
Does NOT look behind logfile rotations, which should not be a problem because it’s closely hooked to dpkg.

/usr/sbin/apt-lastupgrade:

#!/bin/bash

while IFS=: read -r key value
do
	if [[ "${key}" == 'Start-Date' ]]
	then
		upgraded=0
	elif [[ "${key}" == 'Upgrade' ]]
	then
		upgraded=1
	elif [[ "${key}" == 'End-Date' ]]
	then
		if [[ ${upgraded} -eq 1 ]]
		then
			printf -v lastupgrade "%s" "${value}"
		fi
		upgraded=0
	fi
done < /var/log/apt/history.log

if [[ -v lastupgrade ]]
then
	tee /var/log/apt/lastupgrade <<-Here
	# Timestamp of last upgrade: ${lastupgrade}
	Here
	touch -d "${lastupgrade}" /var/log/apt/lastupgrade
fi

/etc/apt/apt.conf.d/90lastupgrade:

DPkg::Post-Invoke {"/usr/bin/systemd-run --on-active=60 /usr/sbin/apt-lastupgrade || /bin/true"};

Path of running shell script, dirname for locating config files, includes etc.

me_path="$(readlink -f "${0}")"
me_dir="$(dirname "${me_path}")"
me_base="$(basename "${me_path}")"

Too Good To, UNIX & Linux

Too good to #0002

10. September 2022 #!/bin/blog 2 Comments

Show and update the comment in an SSH private key

ssh-keygen -l -f <keyfile> # show
ssh-keygen -c -f <keyfile> # change interactively
ssh-keygen -c -C <newcomment> -f <keyfile> # change and provide new

ssh-agent in Gitlab CI/CD

Define SSH_KEY as a “file” in Gitlab CI/CD variables and SSH_PASSPHRASE as a regular variable
If libcrypto errors on execution, make sure SSH_KEY has an additional line ending at the end

before_script:
  - DEBIAN_FRONTEND=noninteractive apt-get update -y
  - DEBIAN_FRONTEND=noninteractive apt-get install -y openssh-client

sftp_to_somewhere:
  stage: deploy
  script:
    - chmod 600 "$SSH_KEY"
    - eval $(ssh-agent)
    - ssh-add "$SSH_KEY" <<< "$SSH_PASSPHRASE"
    - ssh-add -l

Urlwatch, but with a local pop-up window on Linux, no additional infrastructure

Systemd user service:

# ~/.config/systemd/user/urlwatch-to-zenity.service
[Unit]
Description=urlwatch to zenity (service)

[Service]
Type=oneshot
ExecCondition=sh -c 'nmcli net co | grep full'
ExecCondition=sh -c 'urlwatch > %h/.cache/urlwatch.out'
ExecCondition=sh -c 'test -s %h/.cache/urlwatch.out'
ExecStart=sh -c 'zenity --title Urlwatch --text-info --width=600 --height=400 --filename=%h/.cache/urlwatch.out'

[Install]
WantedBy=default.target

Systemd timer:

# ~/.config/systemd/user/urlwatch-to-zenity.timer
[Unit]
Description=urlwatch to zenity (timer)

[Timer]
OnStartupSec=1h
OnUnitInactiveSec=2h

[Install]
WantedBy=default.target

cookiecount – Load a page and show the cookies it sets

$ ./cookiecount https://example.com
0 cookies received.

ps1_anon.bash – anonymize bash prompt, for screenshots and pastes

# Anonymize bash prompt for screenshots and pastes
# Source from or add to ~/.bashrc
function ps1_anon (){
	if [[ -v SAVED_PS1 ]] 
	then
		PS1="${SAVED_PS1}" 
		unset SAVED_PS1 
	else
		SAVED_PS1="${PS1}" 
		PS1='\$ '
	fi
}

Example:

[martin@idefix ~/devel/cookiecount(main=)]$ ps1_anon
$ ./cookiecount https://reddit.com --json | jq .cookiecount
7
$ ps1_anon
[martin@idefix ~/devel/cookiecount(main=)]$

Too Good To, UNIX & Linux

Too good to #0001

5. September 2022 #!/bin/blog

Set X11 keyboard layout manually and temporarily (e.g. in i3 if I need to test exotic window managers for my users)

setxkbmap -layout us,us -variant altgr-intl -option caps:none

Speaking of which, set keyboard layout permanently in Gnome

gsettings set org.gnome.desktop.input-sources sources "[('xkb', 'us+altgr-intl')]"

Check if Gnome Screensaver is active (I use this for automated time tracking)

busctl --user call org.gnome.ScreenSaver /org/gnome/ScreenSaver org.gnome.ScreenSaver GetActive

Urlwatch for a new package version in an APT repository

After a long wait, I was finally able to find another use for my awful Perl one-liner from 2019 that pivots a Debian Packages.gz into a space-separated table!

---
name: "Pop!OS Firefox package"
command: curl -s http://apt.pop-os.org/release/dists/jammy/main/binary-amd64/Packages.gz |
  gzip -dc | perl -ane 'if($F[0]=~/^Package:/){$p=$F[1]};if($F[0]=~/^Version:/){$v=$F[1];print"$p $v\n";}' |
  grep '^firefox '
diff_filter:
  - grep: '^[+-][^+-]'
---

#!/bin/blog

Category Archives: Too Good To

Too good to #0009

Too good to #0008

Too good to #0007

Too good to #0006

Too good to #0005

Too good to #0004

Too good to #0003

Too good to #0002

Too good to #0001

What goes up, must come down. Ask any system administrator.