League of Professional System Administrators - Unix

Notes on accessing SVN over SSH

Aleksey Tsalolikhin — Fri, 26 Sep 2008 12:32:00 -0700


Here are my notes how I set up SVN over SSH to an SVN server that had been set up to run SVN as a single user, "svn".

So, we have multiple users on the remote side, all logging in as "svn" on the SVN server side.
Authentication is done via a dedicated key-pair, with special options to make SVN+SSH work.

See http://svn.collab.net/repos/svn/trunk/notes/ssh-tricks for more details.

These are just my notes, the above link is authoritative.


Procedure:

1. Generate a dedicated key pair

	[SVN Client]$ ssh-keygen -f ~/.ssh/svnssh
	Generating public/private rsa key pair.
	Created directory '/home/tsalolia/.ssh'.

Grub-booting memtest86 on x86 hardware

nomad — Tue, 08 Jul 2008 09:28:24 -0700

It is trivial to set things up so you are able to select memtest86 as a boot option in GRUB:

Download the latest memtest source from http://www.memtest86.com.

Extract and follow the instructions in the README that comes with it to compile. Copy the resulting memtest.bin to /boot and edit /etc/grub.conf to have the following 3 lines:

title Memtest86
        root (hd0,0)
        kernel /boot/memtest.bin

Make sure you reboot to test.

In theory this should work with any x86 OS + bootloader. I am doing this with RHEL 4 + GRUB.

Mixing Multiple Volume Managers (especially ZFS and VxVM)

spp — Mon, 07 Jul 2008 13:15:13 -0700

I've recently had a number of projects at work that want to mix multiple volume managers on a single server, specifically ZFS and VxVM for SAN volumes (actually, three including SVM for internal boot disk mirroring). The projects generally are for database servers, and want to use VxVM for database volumes because ZFS currently has some serious limitation on database size (limited number of devices recommended in a single zpool) and performance (single threaded checksumming, for one). However, at the same time, they want to have access to some of ZFS's features (in particular, the ability to oversubscribe filesystems, dynamic resize, snapshots and rollback) for some of the other filesystems.

Heartbeat / Linux-HA

dlang — Tue, 16 Oct 2007 22:51:19 -0700

Short Description:
Failover and availability clustering for *nix systems

Home Page:
linux-ha.org

Release Date:
Wed, 1998-03-18 10:58

Status:
Mature

Long Description:

Linux-HA aka Heartbeat is a modular package to control high-availability clustering. In spite of it's name it is not limited to Linux (although that is the primary platform), It has an automake based compile and has been used on *BSD, Solaris, and to some extent on AIX as well.

It can hearbeat in multiple ways (UDP broadcast, multicast, and unicast as well as over serial ports, although the serial port heartbeat has been accidently broken in some versions), and over multiple channels (up to 32 as of the time of writing)

It can support sub-second failover

It delays heartbeat checking on initial boot to allow switches time to get through their spanning tree detection timeouts.

Notes on *nix atime

ski — Thu, 09 Aug 2007 12:53:38 -0700

Read an interesting discussion on the lkml list where Linus and friends talked about atime's performance impacts (http://kerneltrap.org/node/14148). Ingo phrased the problem best with:

' For every file that is read from the disk, lets do a ... write to
the disk! And, for every file that is already cached and which we
read from the cache ... do a write to the disk! '

Solutions are to mount your file systems with the noatime, nodiratime options. The only time this may cause a problem is if you have a local mail spool (the mailer will not know that new email arrived) or possibly with some backup software.

ifinput

jm — Fri, 06 Jul 2007 16:12:20 -0700

Short Description:
A wrapper command to run another command if there is any output on stdout

Home Page:
www.generalconcepts.com/resources/software/

Release Date:
Wed, 2001-02-14 15:00

Status:
Stable

Long Description:

Often Unix system administrators need an easy way to redirect any stderr output generated from crontab entries to a specific email address. With the ifinput binary, it's simple. For example:

20 8 * * * /usr/local/sbin/daily_stuff.sh 2>&1 | /usr/local/bin/ifinput mailx -s "Error: daily_stuff.sh" system-errors@foo.org

Just arrange the crontab entries so that the periodic jobs don't generate stdout unless there's something interesting there. Then redirect stderr to stdout and pipe both to ifinput.

ifinput can be used in a variety of different scenarios, not just cron jobs.
The source code is available here: http://www.generalconcepts.com/resources/software/gctools-1.0.tar.gz
It has a very small footprint and will compile without issue on most unix systems.

Bcfg2

nld — Sat, 10 Feb 2007 12:02:18 -0800

Short Description:
Bcfg2 is a centralized configuration tool that provides reconciliation of the current actual configuration with a specification.

Home Page:
trac.mcs.anl.gov/projects/bcfg2

Release Date:
Wed, 2004-10-06 15:48

Status:
Stable

Long Description:

Bcfg2 is a generative configuration management system that can be used for management of aspects of client systems, complete control of client systems, and the range in between. Bcfg2 is designed to work well in pre-existing environments, and in the presence of manual administration.
Bcfg2's most interesting feature is a web frontend that presents client configuration conformance information to administrators. This provides administrators with a direct way to observe how good of a job they are doing describing how their network should look. To our knowledge, this approach is unique to bcfg2, both as a goal and as a supported operation.

Django

eadmund — Mon, 22 Jan 2007 13:08:07 -0800

Short Description:
Excellent Python web development framework

Home Page:
www.djangoproject.com

Release Date:
Fri, 2005-07-15 14:00

Status:
Stable

Long Description:

I like to use this to throw together nice web frontends for the PHBs to look at stats & stuff. It's pretty simple to use, interfaces easily to a database--very useful for the sorts of sysadmin-plus stuff I tend to do.

NMAP

dklein — Sun, 14 Jan 2007 09:50:04 -0800

Short Description:
Fast enumeration of network services

Home Page:
insecure.org/nmap

Release Date:
Sun, 2007-01-14 10:00

Status:
Active

Long Description:

Nmap is a powerful tool for discovering hosts on a network and enumerating what service they are offering. This can be used to find vulnerable systems, to locate rogue services on your network or simply for a first step in troubleshooting.

The latest admin trick I learned...

bwilson — Wed, 20 Dec 2006 08:02:49 -0800

Although LOPSA is platform-agnostic, my current job has me solidly as a Solaris and EMC storage admin. I have experience on just about every other platform of at least a limited extent (DEC UNIX, SCO, HPUX, Windows 4.0, 2000, 2003, Linux mainly RedHat, FreeBSD, OSX, etc...). However all the new tricks I learn, most are going to be on the Solaris platform.

The latest two things I had to learn are how to handle shared memory allocations under Solaris 10, and the 'supported' way to make Veritas filesystems mounted in a zone.

Shared memory was interesting, I mainly googled and asked around until I got a couple of command lines. Then when that didn't work quite as expected in a zone, I borrowed a copy of the new Solaris Internals books to see if I was doing something wrong. Turns out I wasn't really, I just seemed to be running the box out of memory completely.

daemontools

doug — Sat, 21 Oct 2006 21:04:48 -0700

Short Description:
daemontools is a collection of tools for managing UNIX services

Home Page:
cr.yp.to/daemontools.html

Release Date:
Tue, 2000-11-07 21:00

Status:
Mature

Long Description:

daemontools is a collection of tools for managing UNIX services.

supervise monitors a service. It starts the service and restarts the service if it dies. Setting up a new service is easy: all supervise needs is a directory with a run script that runs the service.

multilog saves error messages to one or more logs. It optionally timestamps each line and, for each log, includes or excludes lines matching specified patterns. It automatically rotates logs to limit the amount of disk space used. If the disk fills up, it pauses and tries again, without losing any data.

A less encumbered version is available at http://smarden.org/runit/

Dtrace quick reference

doug — Thu, 21 Sep 2006 12:59:34 -0700

Short Description:
DTrace Quick Reference Guide

Home Page:
developers.sun.com/solaris/articles/dtrace_quickref/dtrace_quickref.html

Release Date:
Thu, 2006-09-21 12:00

Status:
New

Long Description:

DTrace is a comprehensive dynamic tracing facility that is built into the Solaris OS. DTrace can be used by administrators and developers, and can safely be used on live production systems. DTrace enables you to examine the behavior of user programs as well as the behavior of the operating system. Users of DTrace can create custom programs with the D scripting language. Custom programs provide the ability to dynamically instrument the system. Custom programs provide immediate, concise answers to specific questions about the behavior of particular applications.

rsyslog

doug — Sun, 27 Aug 2006 20:47:42 -0700

Short Description:
Rsyslog is an enhanced multi-threaded syslogd supporting, among others, MySQL, syslog/tcp, RFC 3195, permitted sender lists, fil

Home Page:
www.rsyslog.com

Release Date:
Fri, 2005-09-23 20:00

Status:
Active

Long Description:

Rsyslog is an enhanced multi-threaded syslogd supporting, among others, MySQL, syslog/tcp, RFC 3195, permitted sender lists, filtering on any message part, and fine grain output format control. It is quite compatible to stock sysklogd and can be used as a drop-in replacement. Its advanced features make it suitable for enterprise-class, encryption protected syslog relay chains while at the same time being very easy to setup for the novice user. An optional web interface - phpLogCon - can be used to visualize all data online.