(The situation described below has existed for a while, but I don't
believe it has been reported here on bug-tar; let me know if I missed it
somehow.)
Under Ubuntu 16.04/Xenial, there is an "lxcfs" virtual filesystem
installed as part of the distribution:
# findmnt -l /var/lib/lxcfs | cat
TARGET SOURCE FSTYPE OPTIONS
/var/lib/lxcfs lxcfs fuse.lxcfs
rw,nosuid,nodev,relatime,user_id=0,group_id=0,allow_other
Unlike most filesystems, this one continually sets all "stat" timestamps
to the current time:
======
~# date; stat /run /var/lib/lxcfs/ ; sleep 1; echo; stat --format="File: %-15n
Change: %z" /run /var/lib/lxcfs/; sleep 1; echo; stat --format="File: %-15n
Change: %z" /run /var/lib/lxcfs/
Sat Nov 25 01:39:18 EST 2017
File: '/run'
Size: 1280 Blocks: 0 IO Block: 4096 directory
Device: 13h/19d Inode: 2 Links: 33
Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2017-11-24 18:24:15.558154617 -0500
Modify: 2017-11-24 08:59:58.885327800 -0500
Change: 2017-11-24 08:59:58.885327800 -0500
Birth: -
File: '/var/lib/lxcfs/'
Size: 0 Blocks: 0 IO Block: 4096 directory
Device: 26h/38d Inode: 1 Links: 2
Access: (0755/drwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2017-11-25 01:39:18.056606799 -0500
Modify: 2017-11-25 01:39:18.056606799 -0500
Change: 2017-11-25 01:39:18.056606799 -0500
Birth: -
File: /run Change: 2017-11-24 08:59:58.885327800 -0500
File: /var/lib/lxcfs/ Change: 2017-11-25 01:39:19.072317100 -0500
File: /run Change: 2017-11-24 08:59:58.885327800 -0500
File: /var/lib/lxcfs/ Change: 2017-11-25 01:39:20.074869433 -0500
======
When I back up these systems with GNU tar using --one-file-system, I get
the following confusing messages:
======
# tar --create --one-file-system --warning=no-file-ignored --verbose --file
t.tar /var/lib 1>/dev/null
tar: Removing leading `/' from member names
tar: /var/lib/lxcfs/: file is on a different filesystem; not dumped
tar: /var/lib/lxcfs: file changed as we read it
======
Obviously this particular file system is an extreme case, but seeing the
above output at all made me wonder whether it would just generally make
sense for tar to avoid performing the "file changed as we read it" check
for directories that it has just skipped due to the one-file-system
check?
Nathan
----------------------------------------------------------------------------
Nathan Stratton Treadway - natha...@ontko.com - Mid-Atlantic region
Ray Ontko & Co. - Software consulting services - http://www.ontko.com/
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