SageMath Mirror Network

This is a collection of notes on how the mirror network of SageMath operates and a howto on how a mirror is setup. This might be of interest outside SageMath, too. It's only Linux specific.

RSYNC

rsync

  1. is a tool to synchronize a local directory with the contents of a remote directory.
  2. is a server, that provides access to local directories to exchange data using the rsync protocol.

To synchronize with SageMath's master, you can use this command:

rsync -av --delete-after rsync.sagemath.org::sage $TARGET

where $TARGET should be replaced by your local target directory.

NOTE: If you are a new mirror or re-syncing everything, please use

rsync://rsync.mirrorservice.org/www.sagemath.org/

to avoid traffic on the main mirror server. Thank you!

  1. -a switches to archive mode (same timestamp, ...)

  2. -v (or -vv, -vvv) verbosity level, for the lovely logs

  3. --delete-after tells rsync to delete files that are not on the master after the synchronization has finished (i.e. old binary files from the last release). There are also other versions of --delete* that can be used to delete older files earlier or during the process, but it's best if files stay on the mirror during sync. Do not forget one of the --delete* switches to avoid using up more and more disk space!

Other Sources: Since the master is sometimes slow, you can also try to rsync from one of the mirrors:

rsync master

It's dead simple to setup an rsync master server. In Ubuntu/Debian, you have to install rsync and then edit the rsync config file /etc/rsyncd.conf. The inet deamon calls the rsync process if someone wants to connect.

Periodic Checks

At least twice a day, a mirror should check if there are updates on the master. Most of the time there is nothing to do, so it quits fast and nothing happens. If there is a new release, the synchronization starts and it might take some time. Here I describe two techniques, how to avoid concurrent calls of the rsync task in case it takes a bit longer. I use a setup where the mirror checks on every full hour and only runs as one instance.

crontab

cron is a nice system daemon, that does periodic task scheduling in linux. As a regular user, run crontab -e in a terminal to start the crontab editor. A line like

*/10 * * * * "/home/<username>/rsync_sagemath" 2> /home/<username>/rsync_sagemath.errors > /dev/null

calls the rsync_sagemath script every time the minutes in the computer clock are "00" or a multiple of "10" (modulo 10). Something like "0 */2 * * * " does it every second hour when the minutes are "00", "0 1,9,19 * * * " at full hours 1am, 9am and 7pm, ... Read the man crontab page for more information. The part after that just says that errors should be written into a specific file and everything else should be written nowhere.

Beware, there *has* to be a <newline> at the end of the file, not just the crontab line.

A nice addition would be to write the output of the rsync task to a temporary file that is copied into the mirror as a hidden file. Then, the operators of the master server can check, if there were problems with that mirror server!

flock

flock is a utility that ensures, that a certain command is only called once. This is very useful, because the mirror task from above maybe lasts longer than the time interval of the scheduler. The way I use it is the following:

flock -xn ./mirror_sagemath.lock rsync ....
  1. -xn means, that it should grap an eXclusive lock and should Not run, when the task is already running

  2. ./mirror_sagemath.lock is the lock file

  3. then, the entire rsync command ...

No flock ???

It might happen that the debian package linux-utils (that holds flock) is not installed. I found a nice workaround at stackoverflow. This is how I use it:

$ cat rsync_sagemath

# rsyncs from sage.math.washington.edu using its rsync daemon
# for automated use, remove the "vv" and "progress" switches

# locking mechanism from
# http://stackoverflow.com/questions/185451/quick-and-dirty-way-to-ensure-only-one-instance-of-a-shell-script-is-running-at-a
# since flock is not installed :(

cd

LOCKFILE=./rsync_sagemath.lock

if [ -e ${LOCKFILE} ] \&\& kill -0 `cat ${LOCKFILE}`; then
    echo "rsync_sagemath already running ... exit"
    exit
fi

# make sure the lockfile is removed when we exit and then claim it
trap "rm -f ${LOCKFILE}; exit" INT TERM EXIT
echo $$ > ${LOCKFILE}

# actual work
rsync -av --delete-after --partial sage.math.washington.edu::sage /home/<username>/sage/

rm -f ${LOCKFILE}

MirrorNetwork (last edited 2015-05-11 18:53:31 by schilly)