Great answer..you beat me to it.
This is the reason I asked if it was a USB or Firewire drive. When the kernel
driver detects errors on the disk, it will force it into read-only mode.
Very annoying and frustrating if you don't know that it can and will do that to
you. I had this exact problem with the very early Firewire drivers in Linux. It
would write fine a few times, then suddenly become read-only.
________________________________
From: [EMAIL PROTECTED] on behalf of Holger Parplies
Sent: Wed 3/28/2007 8:28 PM
To: Winston Chan
Cc: [email protected]
Subject: Re: [BackupPC-users] Unable to connect to BackupPC server error
Hi,
Winston Chan wrote on 28.03.2007 at 21:04:08 [Re: [BackupPC-users] Unable to
connect to BackupPC server error]:
>>>>> I had been running BackupPC on an Ubuntu computer for several months to
>>>>> back the computer to a spare hard drive without problem. About the time
>>>>> I added a new host (Windows XP computer using Samba), I started getting
>>>>> the following behavior:
first of all, your problem seems unrelated to the new host.
> When I try to touch a file as root, I get "touch: cannot touch
> `/var/lib/backuppc/log/LOG': Read-only file system."
What you're seeing is that your file system is mounted read/write when you
boot your machine, as it should be. BackupPC works. Then something comes
along and remounts the file system read-only. That might crash BackupPC (in
fact, I'd expect it to try to log a fatal error, which won't work, because
it can't write to its log files, and then terminate). What can remount your
file system read-only?
1.) The kernel. It does this if you mount the file system with the option
"errors=remount-ro" or if the option is set in the file system metadata
(and file system corruption is detected during operation, of course :).
You can check with 'tune2fs -l /dev/whatever' (replace /dev/whatever
with the name of the block device your file system is on, see the
output of 'df /var/lib/backuppc', left column, if you're unsure) under
the label "Errors behavior".
Is /var/log on a different partition from /var/lib/backuppc? If so, you
should be able to find a message in /var/log/messages if this happened.
If both are on the same partition, your system log files won't have been
written to after remounting either (which would indicate the approximate
time it happened though).
2.) Some software doing something it's probably not supposed to. I wouldn't
know who should 'mount /var/lib/backuppc -oremount,ro' or the like, but
it's a possibility.
3.) A user pressing <Alt><SysRq><u> at the console. That would affect *all*
file systems however. Remove either these three keys or the user who did
it ;-). Or 'echo 0 > /proc/sys/kernel/sysrq' (see /etc/sysctl.conf if
you really want to do that, but I strongly doubt that is your problem).
> > Wasn't that Windoze, where you occasionally have to reboot because something
> > stops working for no good reason? ;-)
... my point being that, with Linux, instead of rebooting, you'd simply
% mount /var/lib/backuppc -oremount,rw
(presuming /var/lib/backuppc is the relevant mount point), and you'll
probably get an error message stating the file system has errors, which
you'd need to fix with fsck (unmount the file system first!) [I haven't got
a file system with errors available, so I can't check if remounting rw is
really rejected; it might just work despite errors on the FS, so you should
probably run fsck (after unmounting) anyway]. Let's hope it is something that
*can* be reasonably fixed, considering it's grave enough for the kernel to
remount the file system. Rebooting is not a solution in this case, it only
hides the problem until it gets bad enough that all of your pool is lost.
Are, by any chance, regular checks of the file system in question turned off
("Mount count" and "Maximum mount count" in the tune2fs output)?
You should probably try to figure out whether the underlying disk has a
problem (/var/log/messages is your friend and probably the smartmontools) or
if it was only a glitch caused by software or a power failure or a user
failure (you wouldn't believe what I found on my favorite messed up file
system). Presuming you don't simply have a cron job that remounts the file
system every few days :-).
Good luck.
Regards,
Holger
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