Linux Notes: experiments with rsync

  1. The information presented here is intended for educational use by qualified computer technologists.
  2. The information presented here is provided free of charge, as-is, with no warranty of any kind.
Edit: 2020-08-06 (fixed a potential SELinux problem)

rsync (a 3-km / 10,000-foot view)

  • "rsync -a" is a neat alternative to "cp -r"
  • use the "-X" or "--xattrs" switches to also copy meta-data which includes SELinux stuff
  • rsync can be used to do live incremental backups (only copy the files which were added or modified)
    • a more dangerous mode allows rsync to delete destination files which were deleted from the source server
  • rsync is dependent upon SSH so you had better read this first
  • what follows are just extracts of my rsync experiments on a Linux system (running CentOS-7.5) connecting to a Linux system (also running CentOS-7.5) over a private maintenance network running 1 Gb/s

My rsync scripts

#!/bin/bash
# ===================================================================
# title  : neil_rsync_kawc4n_002.sh
# author : Neil Rieck
# created: 2019-09-23
# edit   : 2019-09-26
# edit   : 2020-08-06 (add support for SELinux)
# notes  : 
# 1) copy "some" folders via our private network
# 2) to develop skills for mirroring between Kitchener and Barrie
# 3) be very careful NOT to copy to self <<<---***
#    private network assignments:
#       IPv6   IPv4        host
#       fd::f0 192.168.200 kawc0f (PROD)
#       fd::f1 192.168.201 kawc3v (PROD - hot sync)
#       fd::e0 192.168.190 kawc4n (DVLP)
#       fd::e1 192.168.191 kawc4m (DVLP - hot sync)
# 4) place a public key at the destination to bypass the p/w prompt
# 5) rsync switches:
#    a) think of -a as -r with additional features
#    b) use -X or --xattrs to also copy meta-data including SELinux stuff
#    c) do not use -z on a fast link (compression slows the transfer)
#    d) use -P to see transmit speeds along with file percents
#    e) --bwlimit=125M should saturate a 1Gb/s link (careful!)
#    r) --bwlimit=0    means no limit (careful!)
# ===================================================================
#
#	SAFETY FIRST *** SAFETY FIRST *** SAFETY FIRST
#
#	define variables here to avoid typos below
#
safety="kawc4n"                  # change as required (check this)
#my_switch="-aXP --bwlimit=125M" # settings for a 1Gb/s private link (with percent)
my_switch="-aX --bwlimit=125M"   # settings for a 1Gb/s private link
#my_dest="root@192.168.255.191"  # IPv4 destination (check this)
my_dest="root@[fd::e1]"          # IPv6 destination (check this)
# ===================================================================
echo "-i-script: "$0
echo "-i-caveat: this script may only run on hostname '"${safety}"'"
set -e				# stop on error - VERY IMPORTANT
my_temp=${HOSTNAME}		# could return 'kawc??' or 'kawc??.on.bell.ca'
my_host=${my_temp%%.*}		# discard everything from the first dot onward
if [ ${my_host} == ${safety} ];
then
    echo "-i-okay to run on host: "${my_temp}
else
    echo "-e-not okay to run on host: "${my_temp}" so exiting"
    exit			# adios
fi
# ===================================================================
# copying begins
# ===================================================================
echo "-i-starting"
date
echo "task 1"
# -------------------------------------------------------------------
# copy web content to a remote machine (do not overwrite placeholder
# files already running there so choose a different folder)
#
# src:	  /var/www
# dst:    /backup/
# result: /backup/www/
# notes:
# 1) src - no trailing slash says to copy var and everything under it
# 2) dst - a trailing slash here means /backup must already exist on the
#          remote machine AND it is okay to create sub-directories
# 3) examples:
#    rsync -azPX	/var/www	root@192.168.255.191:/backup/
#    rsync -azPX	/var/www	root@[fd::e1]:/backup/
# -------------------------------------------------------------------
#
#	other important stuff
#
echo "task 2"
rsync ${my_switch}	/var/www	${my_dest}:/backup/
rsync ${my_switch}	/usr/local	${my_dest}:/backup/
rsync ${my_switch}	/etc		${my_dest}:/backup/
rsync ${my_switch} -P --delete /var/lib/maria-backups ${my_dest}:/backup/
#
#	copy "/home" part-3.1	(these three are copied in pieces)
#
echo "task 3.1"
rsync ${my_switch}	/home/neil	${my_dest}:/home/
rsync ${my_switch}	/home/dave	${my_dest}:/home/
rsync ${my_switch}	/home/vince	${my_dest}:/home/
#
#	copy "/home" part-3.2	(copy anything else here: mamgrp, etc.)
#
echo "task 3.2"
rsync ${my_switch} -P	/home		${my_dest}:/
#
#	scripts and utilities in /root
#	question: what would happen if we copy everything under .ssh (???)
#	Would it destroy files like identity and authorized_keys at the other side?
#
echo "task 4"
rsync ${my_switch}	/root/*.sh	${my_dest}:/root/
rsync ${my_switch}	/root/*.txt	${my_dest}:/root/
rsync ${my_switch}	/root/ssa*	${my_dest}:/root/
# ===================================================================
echo "-i-finished"
date
# ===================================================================

My New Block Diagram

   PROD (Linux)          DVLP (Linux)       other systems 
+-----------------+ +-----------------+ +-------------------+
| primary         | | primary         | | 4 OpenVMS systems |
+-----------------+ +-----------------+ +-------------------+

+-----------------+ +-----------------+ +-------------------+
| local stand by  | | local stand by  | | 2 Solaris systems |
+-----------------+ +-----------------+ +-------------------+

+-----------------+ +-----------------+
| remote stand by | | remote stand by |
+-----------------+ +-----------------+ 
  • primary employs rsync to copy to local stand by (same data facility) several times a day
  • primary employs rsync to copy to remote stand by (a different city more than 100-km away) several times a day
  • All Linux systems are currently running CentOS-7.7 with Apache and MariaDB
    • having a local stand by can provide peace of mind when you wonder if the next YUM update might break something
    • unlike Amazon or Alibaba, these systems do very little between 21:00 and 8:00
    • this scheme is also useful when migrating to newer server hardware
  • The box labeled "4 other systems" are OpenVMS platforms
    • these machines used to do daily backups to tape which were delivered off site (M-F, excluding holidays)
    • Now, these machines copy their backups into a folder on "DVLP Linux primary" which are then rsync'd to local standby and remote standby every day

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Neil Rieck
Waterloo, Ontario, Canada.