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On 11.09.2011 18:19, Robert Kawecki wrote:
> ZNC uses an exclusive lock on a file handle that is open read-only. This
> operation is not supported on NFSv4, as described here:
> http://www.spinics.net/lists/linux-nfs/msg18594.html
> This problem makes znc unusable on NFSv4-mounted home directories, resulting
> in
> error message:
> [ !! ]is already running on this config. ]
> (since it can't lock the file, it assumes someone else did!)
>
> Relevant output of "strace -e open,flock znc":
> open("/home/users/thewanderer/.znc/configs/znc.conf", O_RDONLY) = 3
> flock(3, LOCK_EX|LOCK_NB) = -1 EIO (Input/output error)
Hi,
Welcome to the wonderful world that is file locks. To quote "man 2 flock":
A shared or exclusive lock can be placed on a file regardless of the mode in
which the file was opened.
So technically a NFS bug, if you ask me.
> I see two solutions:
> 0) Implement proper error checking when locking the config file. EIO is not
> equal to EWOULDBLOCK!
How would that help? Instead of "znc is already running on this config", startup
would fail with "Could not lock config".
> 1) Use a writable file, like znc.conf.lock (config file path with ".lock"
> suffix appended), for exclusive locks.
(Just znc.conf is fine, too, since ZNC rewrites its config regularly and thus
needs write access to it anyway)
Since SVN rev 2065 / git commit 33ce80f476be797a / ZNC 0.094, ZNC uses fcntl()
instead of flock() for file locks. This change was done for Solaris, but AFAIK
this should also make NFS happy.
Relevant strace output:
write(1, "\33[1m\33[34m[\33[32m \33[34m]\33[39m\33["..., 92[ ] Opening
Config [/home/psychon/.znc/configs/znc.conf]... ) = 92
stat("/home/psychon/.znc/configs/znc.conf", {st_mode=S_IFREG|0600, st_size=2098,
...}) = 0
stat("/home/psychon/.znc/configs/znc.conf", {st_mode=S_IFREG|0600, st_size=2098,
...}) = 0
open("/home/psychon/.znc/configs/znc.conf", O_RDWR) = 3
fcntl(3, F_GETFD) = 0
fcntl(3, F_SETFD, FD_CLOEXEC) = 0
fcntl(3, F_SETLK, {type=F_WRLCK, whence=SEEK_SET, start=0, len=0}) = 0
lseek(3, 0, SEEK_SET) = 0
read(3, "// WARNING\n//\n// Do NOT edit thi"..., 4096) = 2098
read(3, "", 4096) = 0
Cheers,
Uli
- --
"Do you know that books smell like nutmeg or some spice from a foreign land?"
-- Faber in Fahrenheit 451
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