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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for the ‘Linux’ Category

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TL;DR: Raspberry Pi models 1..3 become hotter and hotter under load; no housing gives best cooling.

Posted by jpluimers on 2020/02/04

[WayBack] TIL Raspi Kühlkörper bringen nix. Lego schon.  – Kristian Köhntopp – Google+

Background information: [Archive.is] Mein Raspberry Pi 3 und sein Problem mit der Systemtemperatur · Un*xe

–jeroen

 

Posted in *nix, Debian, Development, Hardware, Hardware Development, Linux, Power User, Raspberry Pi, Raspbian | Leave a Comment »

OpenSuSE: location of cron jobs

Posted by jpluimers on 2020/01/20

When you look at how to find listed cron jobs, usually the answer is cron -l or cron -u username -l.

However, on OpenSuSE systems, cron jobs can be in different places, and the sysconfig settings have influence on them too.

These files and directories all influence cron:

Directories:

/etc/cron.d/
/etc/cron.daily/
/etc/cron.hourly/
/etc/cron.monthly/
/etc/cron.weekly/

Files:

/etc/sysconfig/cron
/etc/init.d/rc2.d/K01cron
/etc/init.d/rc2.d/S14cron
/etc/init.d/rc3.d/K01cron
/etc/init.d/rc3.d/S14cron
/etc/init.d/rc5.d/K01cron
/etc/init.d/rc5.d/S14cron
/etc/init.d/cron
/etc/news/crontab.sample
/etc/pam.d/crond
/etc/systemd/system/multi-user.target.wants/cron.service
/etc/omc/srvinfo.d/cron.xml
/etc/cron.deny
/etc/crontab

Most are available for other Linux distributions as well, but each one might have slightly different configurations (especially for the directories). Some background reading:

Some details:

  • The crontab -l will only list what is in /etc/crontab.
  • These directories are influenced by/etc/sysconfig/cron, especially the DAILY_TIME variable (see below) for the daily jobs.
    All of the directories are checked every 15 minutes through /usr/lib/cron/run-crons:/etc/cron.daily/
    /etc/cron.hourly/
    /etc/cron.monthly/
    /etc/cron.weekly/
  • That script then uses these files for checking when to run:/var/spool/cron/lastrun/cron.weekly
    /var/spool/cron/lastrun/cron.daily
    /var/spool/cron/lastrun/cron.hourly

The DAILY_TIME variable:

## Type: string
## Default: ""
#
# At which time cron.daily should start. Default is 15 minutes after booting
# the system. Example setting would be "14:00".
# Due to the fact that cron script runs only every 15 minutes,
# it will only run on xx:00, xx:15, xx:30, xx:45, not at the accurate time
# you set.
DAILY_TIME=""

–jeroen

 

Posted in *nix, *nix-tools, cron, Linux, openSuSE, Power User, SuSE Linux, Tumbleweed | Leave a Comment »

a perf cheat sheet from @brendangregg’s fantastic web page;  you can print it as PDF

Posted by jpluimers on 2020/01/13

From a while back: [WayBack] ⚡Julia Evans⚡ on Twitter : made a perf cheat sheet from @brendangregg’s fantastic brendangregg.com/perf.html you can print it at …

References:

The latter has a lot of examples and even more explanation all around the below picture.

–jeroen

Read the rest of this entry »

Posted in *nix, *nix-tools, Development, Linux, Power User, Profiling-Performance-Measurement | Leave a Comment »

Magic SysRq key – Wikipedia

Posted by jpluimers on 2019/12/20

Cool: Magic SysRq key – Wikipedia

The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low-level commands regardless of the system’s state. It is often used to recover from freezes, or to reboot a computer without corrupting the filesystem.[1] Its effect is similar to the computer’s hardware reset button (or power switch) but with many more options and much more control.

Sometimes reading fluffy fluff posts teaches you new things, so be sure to read this one:

[WayBack] I just got trolled by my cat, hard. Last night i left my linux laptop open and running while watching TV in the other room. I came back to find Marley … – Stephen Shirley – Google+

…

I started looking through the kernel logs from last night, to see if there was any indication of the issue starting. And then i saw it. One innocent line that said:

Dec 18 21:26:52 x240 kernel: [373001.156356] sysrq: SysRq : Emergency Remount R/O

The fluffy dumbass had somehow hit the Sysrq [0] key combo to mount all filesystems read-only. This is an old, low-level when-all-else-fails facility for dealing with an linux unresponsive system, and fluff-for-brains Marley had somehow hit alt+fn+s+u.

Sigh.

[0] https://en.wikipedia.org/wiki/Magic_SysRq_key

Via: [Archive.is] I just got trolled by my cat, hard. Last night i left my linux laptop open and running while watching TV in the other room. I came back to find Marley … – Kristian Köhntopp – Google+

–jeroen

Posted in *nix, *nix-tools, Keyboards and Keyboard Shortcuts, Linux, Power User | Leave a Comment »

Fixing bind named messages like `lame-servers: network unreachable resolving ‘c.gtld-servers.net/AAAA/IN’: 2001:500:127::30#53`

Posted by jpluimers on 2019/11/15

When you see messages like below in your bind named.d logs then you’ve a Jekyll and Hyde network config: part of it says it supports IPv6, but in reality doesn’t as “2001:500:127::30” is the IPv6 of the generic TLD servers.

In my case a brain-dead TP-Link switch.

04-Dec-2016 13:05:48.008 lame-servers: network unreachable resolving 'c.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.008 lame-servers: network unreachable resolving 'd.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.008 lame-servers: network unreachable resolving 'e.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.008 lame-servers: network unreachable resolving 'f.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.008 lame-servers: network unreachable resolving 'g.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.009 lame-servers: network unreachable resolving 'h.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.009 lame-servers: network unreachable resolving 'i.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.009 lame-servers: network unreachable resolving 'j.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.009 lame-servers: network unreachable resolving 'k.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.009 lame-servers: network unreachable resolving 'l.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
04-Dec-2016 13:05:48.009 lame-servers: network unreachable resolving 'm.gtld-servers.net/AAAA/IN': 2001:500:127::30#53
...
04-Dec-2016 13:24:13.500 lame-servers: network unreachable resolving './NS/IN': 2001:500:2f::f#53

A temporary solution is to run bind named.d in -4 mode (see examples for RHEL, CENTOS and OpenSuSE in the links below), but the actual solution is to get IPv6 working properly.

–jeroen

Posted in *nix, bind-named, Linux, Power User | Leave a Comment »

OpenSuSE: the relation between /etc/var/named.d and /var/lib/named

Posted by jpluimers on 2019/10/24

For first time BIND named users on OpenSuSE there is often confusion on the relation between these directories:

  • /etc/named.d/
  • /var/lib/named/

For example here someone else struggled: [WayBack] Re: Fwd: Re: [opensuse] Split DNS? Solved

This is how I inferred the workings:

The /etc/named.conf.include is re-generated at named start by running /usr/share/bind/createNamedConfInclude by including files that both match NAMED_CONF_INCLUDE_FILES in /etc/sysconfig/named and exist in the /etc/named.d/ directory.

At named startup, it also copies everything from /etc/named.d to /var/lib/named/etc/named.d

For details see

–jeroen

Posted in *nix, *nix-tools, bind-named, Linux, openSuSE, Power User, SuSE Linux | Leave a Comment »

zabbix on Windows: check the configuration before restarting the Zabbix Agent service

Posted by jpluimers on 2019/09/27

If the Zabbix configuration on Windows (especially mismatches in C:\zabbix\zabbix.agentd.conf.d), then the Zabbix Agent will not start at all:

C:\zabbix\bin\win64>zabbix_agentd.exe --start
zabbix_agentd.exe [4711]: ERROR: cannot start service [Zabbix Agent]: [0x0000041D] The service did not respond to the start or control request in a timely fashion.

This is how to check it before starting the service:

C:\zabbix\bin\win64\zabbix_agentd.exe --config C:\zabbix_agentd.conf
zabbix_agentd.exe [43]: ERROR: cannot add user parameter "MyDuplicate[*],PowerShell.exe -File C:\zabbix\UniquePowerShellScript.ps1 "$1"": key "MyDuplicate" already exists

The problem is that in the C:\zabbix\zabbix.agent.conf.d directory, two files had a similar config:

UserParameter=MyDuplicate[*],PowerShell.exe -File C:\zabbix\FirstPowerShellScript.ps1 "$1"
UserParameter=MyDuplicate[*],PowerShell.exe -File C:\zabbix\SecondPowerShellScript.ps1 "$1"

The problem is that the first part of UserParameter (before the [*])  is a key which needs to be unique over all configuration files.

If everything is fine, you will see this:

C:\zabbix\bin\win64\zabbix_agentd.exe --config C:\zabbix_agentd.conf
zabbix_agentd.exe [1581]: use foreground option to run Zabbix agent as console application

If you need to manually start Zabbix as a service, then perform this (the first step is not needed if the service has already been stopped):

C:\zabbix\bin\win64>zabbix_agentd.exe --stop
zabbix_agentd.exe [1642]: service [Zabbix Agent] stopped successfully

C:\zabbix\bin\win64>zabbix_agentd.exe --start
zabbix_agentd.exe [1642]: service [Zabbix Agent] started successfully

–jeroen

Posted in *nix, Linux, Monitoring, Power User, Windows, Zabbix | Leave a Comment »

Eigenes DynDNS mit Bind und Apache – CupRacer.de

Posted by jpluimers on 2019/09/16

Dieser Artikel beschreibt, wie man einen eigenen Mechanismus für DNS-Updates als DynDNS-Alternative aufbaut.

Translated:

This article describes how you can create your own mechanism for DNS-updates as alternative for DynDNS.

Interesting read: [WayBack] Eigenes DynDNS mit Bind und Apache – CupRacer.de

Edit

The above post disappeared, but this one (which adds calling the DynDNS server from a Fritz!Box) is still up: [WayBack] Eigener DynDNS mit Bind, Apache und PHP | onderka.com with an update at [WayBack] Eigener DynDNS mit dnsmasq, Apache und PHP | onderka.com.

Source code for both:

Related and background reading:

–jeroen

Posted in *nix, bind-named, Linux, openSuSE, Power User, SuSE Linux, Tumbleweed | Leave a Comment »

Signal messaging downloads

Posted by jpluimers on 2019/08/23

I forgot about the announcement that Signal had also become available on the Desktop, but it is via [WayBack] https://signal.org/download/:

  • Mac
  • Windows
  • Debian based x64 Linux:

$ curl -s https://updates.signal.org/desktop/apt/keys.asc | sudo apt-key add -
$ echo "deb [arch=amd64] https://updates.signal.org/desktop/apt xenial main" | sudo tee -a /etc/apt/sources.list.d/signal-xenial.list
$ sudo apt update && sudo apt install signal-desktop

I like the mix of echo and tee to update the [WayBack] /etc/apt/sources.list.d folder with the signal-xenial.list file.

These links will always give you the latest download filename:

The files you get there will be relative to the path https://updates.signal.org/desktop/ so will be similar to:

You can get the sources at https://github.com/WhisperSystems/Signal-Desktop/releases

Via:

–jeroen

Posted in *nix, Android Devices, Apple, Debian, iMac, iOS, iPhone, Linux, Mac, Mac OS X / OS X / MacOS, MacBook, MacBook Retina, MacBook-Air, MacBook-Pro, MacMini, macOS 10.12 Sierra, Power User, Windows | Leave a Comment »

Introduction to Snapshots/Rollback with Snapper | ActiveDoc

Posted by jpluimers on 2019/07/01

The snapper documentation itself is big and hard to grasp at once, so start here for a few examples on how to get going, or how to assess your current configuration:

For a very good snapper introduction seems to be gone, but was present in the OpenSuSE documentation archive circa version 13.2 at [WayBack] Chapter 4. Snapshots/Rollback with Snapper | ActiveDoc which I’ve quoted below.

Between that version and LEAP, the retention got moved from “timeline” based to “number” based. More on that in these links:

Man pages:

Introduction

4.1.1 snapshots and Disk Space #

When a snapshot is created, both the snapshot and the original point to the same blocks in the file system. So, initially a snapshot does not occupy additional disk space. If data in the original file system is modified, changed data blocks are copied while the old data blocks are kept for the snapshot. Therefore, a snapshot occupies the same amount of space as the data modified. So, over time, the amount of space a snapshot allocates, constantly grows. As a consequence, deleting files from a Btrfs file system containing snapshots may not free disk space!

Note: Snapshot Location

Snapshots always reside on the same partition or subvolume that has been snapshotted. It is not possible to store snapshots on a different partition or subvolume.

As a result, partitions containing snapshots need to be larger than “normal” partitions. The exact amount strongly depends on the number of snapshots you keep and the amount of data modifications. As a rule of thumb you should consider using twice the size than you normally would.

Tip: Freeing space / Disk Usage

In order to free space on a Btrfs partition containing snapshots you need to delete unneeded snapshots rather than files. Older snapshots occupy more space than recent ones.

Since the df does not show the correct disk usage on Btrfs file systems, you need to use the command btrfs filesystem df MOUNT_POINT. Displaying the amount of disk space a snapshot allocates is currently not supported by the Btrfs tools.

–jeroen

Posted in *nix, Linux, openSuSE, Power User, SuSE Linux, Tumbleweed | Leave a Comment »

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