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

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Archive for the ‘Linux’ Category

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 https://t.co/SBDtzn0G8J. you can print it at https://t.co/xC6ndjrSDL https://t.co/TstbBBe3DS

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: [WayBackRe: 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 »

 
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