Comments on: How NOT to test that mysqld is alive

By: Vitlalie Cherpec

Vitlalie Cherpec — Wed, 06 Jan 2010 11:43:37 +0000

I’m using Nagios (http://www.nagios.org/) to monitor mysql servers. Reinventing the wheel is too error prone, just stick with stable and tested solutions. If Nagios itself is too complex, Nagios plugins can be used from scripts. :

Usage help for check_mysql plugin:

[vitalie@shark ~]$ /usr/lib64/nagios/plugins/check_mysql –help

check_mysql v2034 (nagios-plugins 1.4.13)
Copyright (c) 1999-2007 Nagios Plugin Development Team

This program tests connections to a mysql server

Usage: check_mysql [-d database] [-H host] [-P port] [-s socket]
[-u user] [-p password] [-S]

[...]

By: ajd4096

ajd4096 — Thu, 08 Oct 2009 06:23:44 +0000

/proc is not deprecated (nor depreciated) on HP-UX, it never had it, AFAIK.

FreeBSD/OpenBSD/NetBSD have a procfs, but it is not mounted by default.

(The main reason for avoiding procfs is that reading from /proc in user-space suffers from TOCTOU, whereas a system call does not. This issue was raised yet again on the OpenBSD misc@ mailing list only a few weeks ago.)

There is a procfs for OSX, it’s MacFUSE-based, not from Apple, and not even installed by default.

Obviously there is a sizeable percentage of unix systems where a script referring to /proc will not work.

Now, about the ubiquity of that “bash” shell….

By: Zach

Zach — Wed, 07 Oct 2009 13:33:21 +0000

@FredV

you are totally incorrect, /proc is not in every Unix… /proc has been depreciated in older SysV style OS’es… like ..wait for it… HPUX!

By: FredV

FredV — Wed, 07 Oct 2009 07:29:07 +0000

“/proc is not a standard Unix feature, nor is bash.”

that’s why every unix has it?

By: ajd4096

ajd4096 — Wed, 07 Oct 2009 03:46:32 +0000

@FredV
/proc is not a standard Unix feature, nor is bash.

There is more to unix than the linux distro du-jour.

By: FredV

FredV — Tue, 06 Oct 2009 18:57:14 +0000

Adam: using /proc (a standard Unix feature) and bash-compatible shell script is not portable and brittle? i disagree. asfor extensible: who on earth would want to build something on top and exapand on this? It’s a quick hack anyway, normally you shouldn’t have to do stuff like this.

btw. using /proc, which is *not* as stupid as grepping ps output without even using awk to split into columns. a process can change how it’s displayed in ps by changing argv[0], so the /proc solution I gave is actually the only one that will always work and not brittle as you say

By: Adam Nelson

Adam Nelson — Tue, 06 Oct 2009 15:48:42 +0000

I’m a little disturbed by all the people still posting ps and proc options.

It’s fun that these tricks can be done, but any of that type of custom scripting is not extensible, rarely portable, and highly brittle under a panoply of eventualities.

I know there are systems that have been up for 10 years on this kind of stuff, but it’s not responsible for such band-aids to be allowed to be permanent (or for SysAdmins to think that those are real, proper solutions).

By: ajd4096

ajd4096 — Tue, 06 Oct 2009 09:56:27 +0000

Install MySQL Enterprise Monitor!

Note that it runs a separate instance of mysqld, so “ps|grep|wc” tricks are suddenly useless.

Not that they ever were a good trick, for a number of reasons.
* The race condition mentioned does occur.
* “ps -C” is not portable.
* Processes hang sometimes, functional testing is required.
* Monitoring “foo” should not break when “bar” is run, if/even when “bar” is “foo2″.

By: FredV

FredV — Tue, 06 Oct 2009 08:02:38 +0000

looks like some sysadmin wannabe does not even know how to use awk and regular expressions, any kid should see the holes in that solution

for procf in /proc/[0-9]*; do
if [ "$(cat $procf/exename)" = "/usr/bin/mysqld" ]; then
echo “process is running”
fi
done

By: shlomi

shlomi — Tue, 06 Oct 2009 06:42:26 +0000

@sharks
I agree, please re-read the last paragraph in my post.
Please also note the duality within mysql: “mysqladmin ping” conencts via socket etc., while “mysqld status” checks for pid file and process id.

Regards