Various Linux things

Table of Contents

related linuxinfra

docker linuxdocker

[2018-06-15] docker system prune to cleanup linuxdocker

[2021-01-12] figuring out what takes disk space docker images | awk '{print $3}' | xargs docker inspect | less linuxdocker

[C] [2021-02-12] Docker compose port mapping - Stack Overflow linuxdocker

If you want to bind to the redis port from your nodejs container you will have to expose that port in the redis container:

version: '2'
      context: .
      dockerfile: DockerFile
      - "4000:4000"
      - redis
      context: .
      dockerfile: Dockerfile-redis
      - "6379"
The expose tag will let you expose ports without publishing them to the host machine, but they will be exposed to the containers networks.

[B] [2021-04-14] apt-get clean and other strategies for keeping image size small? · Issue 35 · rocker-org/rocker linuxdocker

ok, so for debian/ubuntu images don't really need autoclean – it's already run automatically

[C] [2021-05-02] Attach and Detach from Docker Container | HowToProgram linuxdockerdrill

In general, to detach from a Docker container and leave it running, we can use the CTRL-p CTRL-q key sequence.

systemd linuxsystemd

debugging: systemctl --failed, journalctl linuxsystemd

logs – for individual jobs you can see them via status (or sdj)
presistent is not showing anythin by default?

profiling: systemd-analyze blame linuxsystemd

use asserts in unit definitions linuxsystemd

  • AssertPathExists fails if the pass is missing or symlink is broken

networking linuxnetwork

who uses local port linuxnetwork

sudo ss -tulpn | grep 5060
sudo ss -anpt  | grep 8640

testing if port is open linuxnetwork

netcat -l 5559

one the other machine

echo "TEST" | netcat host 5559

[2020-06-15] linux - Test if a port on a remote system is reachable (without telnet) - Super User linuxnetwork

Nice and verbose! From the man pages.
Single port:
nc -zv 80

testing if port is open

apt linux

install build dependencies: sudo apt-get build-dep package linux

cron linuxcron

[2018-02-26] if cron fails to start a job, it will send the output to local mail linuxcron

grep cron /var/log/syslog
tail -f /var/log/syslog | grep cron

[2018-05-10] mail subject – use bash comment operator linuxcron

*:* TestJob; cron command

mind the space after colon!

sandboxing linuxsandbox

docker is excellent for quick sandboxes (just use ubuntu:latest image or something) linuxsandboxdocker

firejail for network sandbox linuxsandboxnetworktesting

  • doesn't require root!
  • firejail --noprofile --net=none

udev linuxudev

udevadm info /dev/sdc2 linuxudev

[2019-03-07] when you update rules file sudo udevadm control --reload-rules linuxudev

[2019-03-07] to trigger the target script sudo udevadm trigger linuxudev

[C] [2017-05-08] Gateway means that the subnet is link-local i.e. there is no gateway involved, the packets are delivered directly to the target linuxnetwork

----------------------------------------- linux

[C] [2018-06-08] Linux ignores the setuid bit on all interpreted executables (i.e. executables starting with a #! line). linux

ok apparently setuid shell scripts are quite risky…

[C] [2020-01-29] linux - How to make htop sort by PID linux

press > and select RES

[C] [2020-01-24] logs - View stdout/stderr of systemd service linuxsystemd

Note that using the standard logging mechanism like this will not create persistent logs by default. To do that, you'll need to create /var/log/journal, and then run sudo systemctl restart systemd-journald

[C] [2020-01-29] How to read memory usage in htop? - Server Fault linuxdrill

Hide user threads (shift + H) and close the process tree view (F5), t

[D] [2020-12-04] linux - prevent system freeze/unresponsiveness due to swapping run away memory usage - Super User linux

If a process demands a lot of memory, the system moves all other process to the swap file. Including it seems, necessary processes like the X11 server or the terminal.

[D] [2018-04-27] guide to XKB linux

------------------------------------------- linux

TODO [C] whereis command linuxhabit

CREATED: [2021-04-26]

[C] [2021-05-08] ip - List ports a process PID is listening on (preferably using iproute2 tools)? - Unix & Linux Stack Exchange linux

sudo netstat -plnt
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