#1636 PR closed: Follow symbolic link with COPY_AS_IS targets

Labels: won't fix / can't fix / obsolete, minor bug

gdha opened issue at 2017-12-08 10:36:

  • added the "-h" option to tar to follow the symbolic links
    instead of adding just the symbolic link to the tar archive
    We run into this issue with /etc/localtime (issue #1635)
  • commented out in skel/default/etc/scripts/dhcp-setup-functions.sh
    the localtime copy lines (as the /usr/share/zoneinfo is not
    present anyway in the rescue environment)

gdha commented at 2017-12-08 10:37:

I think this is serious enough to still push it into the release 2.3, agree?

jsmeix commented at 2017-12-08 11:38:

As far as I see this is a backward incompatible change
because without '-h' tar copies symbolic links as symbolic links
so that there can be symbolic links in the recovery system
while with '-h' tar copies the files symbolic links point to
so that there can be no longer symbolic links in the recovery system
which might blow up the recovery system with several copies
of the same (possibly big) file where several symbolic links
point to on the original system.

I fear such a backward incompatible change will cause
unexpected and unwanted bad side effects in this or that
unforeseen special cases.

Couldn't the actual issue https://github.com/rear/rear/issues/1635
be solved with a specific solution only for that issue e.g. like

localtime_link_target="$( readlink -e /etc/localtime )"
COPY_AS_IS=( "${COPY_AS_IS[@]}" /etc/localtime "$localtime_link_target" )


On my SLES11 system:

# ls -l /etc/localtime
-rw-r--r-- 3 root root 2335 Jun 17  2015 /etc/localtime

# readlink -e /etc/localtime

On my SLES12 system:

# ls -l /etc/localtime
lrwxrwxrwx 1 root root 35 Jul 28 10:40 /etc/localtime -> ../usr/share/zoneinfo/Europe/Berlin

# readlink -e /etc/localtime

jsmeix commented at 2017-12-08 12:01:

I even found some broken symbolic links in the recovery system:

# for l in $( find /tmp/rear.n8XNBDuAB0fhlXn/rootfs -xtype l ) ; do file $l ; done
/tmp/rear.n8XNBDuAB0fhlXn/rootfs/etc/localtime: broken symbolic link to `../usr/share/zoneinfo/Europe/Berlin'
/tmp/rear.n8XNBDuAB0fhlXn/rootfs/dev/device-mapper: broken symbolic link to `mapper/control'
/tmp/rear.n8XNBDuAB0fhlXn/rootfs/dev/char/10:236: broken symbolic link to `../mapper/control'

jsmeix commented at 2017-12-08 13:05:

The change

--- a/usr/share/rear/build/GNU/Linux/100_copy_as_is.sh
+++ b/usr/share/rear/build/GNU/Linux/100_copy_as_is.sh

-if ! tar -v -X $copy_as_is_exclude_file -P -C / -c "${COPY_AS_IS[@]}" 2>$copy_as_is_filelist_file | tar $v -C $ROOTFS_DIR/ -x 1>/dev/null ; then
+if ! tar -v -X $copy_as_is_exclude_file -h -P -C / -c "${COPY_AS_IS[@]}" 2>$copy_as_is_filelist_file | tar $v -C $ROOTFS_DIR/ -x 1>/dev/null ; then

has horrible consequences on my SLES12 test system:

Now "usr/sbin/rear -D mkrescue" takes ages at
"Copying files and directories" so that I aborted it
and the recovery system size before was 208M
but with that change (and aborted "Copying files and directories")
it became 1.8G

schlomo commented at 2017-12-08 13:17:

I would like to caution against this change: IMHO symlinks should be copied as-is into the rescue system and not converted into files or directories. IMHO the danger to mess up the system is way too big and especially the danger to bloat up the rescue image (as @jsmeix observed). I think that in most cases the symlinks were put in place purposefully so that we should leave them as there were intended.

For the few known cases where this is a problem we should add extra code to handle it, e.g. /etc/localtime.

If you want to help with finding such places then I would suggest to add code that checks symlinks and reports broken symlinks, especially if they were not broken in the source system.

jsmeix commented at 2017-12-08 13:31:

With the added '-h' it seems "rear mkrescue" even hangs up at
"Copying files and directories" because since several minutes
the ReaR log file stays at

# tail /root/rear.master/var/log/rear/rear-f48.log
++ tar -v -C /tmp/rear.9h061udK1yV7mTo/rootfs/ -x
++ tar -v -X /tmp/rear.9h061udK1yV7mTo/tmp/copy-as-is-exclude -h -P -C / -c /root/rear.master/usr/share/rear /root/rear.master/var/lib/rear /dev /etc/inputrc ...
tar: Removing leading `/' from member names
tar: Removing leading `/' from hard link targets

The recovery system does no longer grow noticeable
because since several minutes it stays at 1.8G

# du -hs /tmp/rear.9h061udK1yV7mTo/rootfs/
1.8G    /tmp/rear.9h061udK1yV7mTo/rootfs/

but when counting bytes one can see it still grows slowly:

# for i in 1 2 3 ; do date +%T ; du -bs /tmp/rear.9h061udK1yV7mTo/rootfs/ ; sleep 10 ; done
1739527435      /tmp/rear.9h061udK1yV7mTo/rootfs/
1739533555      /tmp/rear.9h061udK1yV7mTo/rootfs/
1739541339      /tmp/rear.9h061udK1yV7mTo/rootfs/

so that something is still creeping on...
...after more than half an hour I aborted it again
and got:

# date +%T ; du -bs /tmp/rear.9h061udK1yV7mTo/rootfs/
1740243069      /tmp/rear.9h061udK1yV7mTo/rootfs/

gdha commented at 2017-12-11 07:57:

Good that I asked your opinion! As issue #1638 has been made to tackle this I will close this PR without merging. We can solve it differently.

jsmeix commented at 2018-10-09 09:24:

I documented that symbolic links must be copied as symbolic links
(i.e. why 'tar -h' must not be used for COPY_AS_IS).

[Export of Github issue for rear/rear.]