You basically already showed how to do it on Linux: inside your Go prog,
you know the file descriptor number (f.Fd()). Then do an
os.Readlink(fmt.Sprintf("/proc/self/fd/%d", f.Fd()) and check the result
(if no error) with strings.HasSuffix(link, "(deleted)").
On Sunday, December 10, 2023 at 5:41:00 PM UTC+1 Jason E. Aten wrote:
> I'm debugging a weird situation where my open binary log file
> has been deleted and replaced by an
> identical copy by my doing a git commit (and maybe git rebase)
> on it. The Go process is still running, still has the origional
> file handle open, and is still "writing" to the
> deleted log file to no effect (no further appends are happening).
>
> The /proc listing shows the Go process's file handle to the file as
> (deleted). See below.
>
> My question is: is there a way to have the Go process detect if the file
> it is writing to has been deleted by another process (git in this case) so
> that attempting to append to the file is no longer effective? This example
> is on Linux on xfs filesystem; Ubuntu 18.04. I suppose I could Sync then
> Stat the file before and after and if it is not growing by the appropriate
> number of bytes, take corrective action... but I wonder if there is a more
> elegant way?
>
> go version go1.21.2 linux/amd64
>
> Fortunately I noticed this before too much had gone missing to the
> binary log, and was able to confirm that it was going missing by comparing
> to a textual version of the log that I also keep.
>
> I would be happy to check the file descriptor on each append operation, to
> ensure that the logging will be effective. But writes are succeeding to the
> deleted file: I am checking the error returned by the os.File.Write()
> operation, and it is always nil indicating no error on the Write.
>
> ~~~
>
> myuser*@*host* /proc/94913/fd $* *ls -al*
>
> total 0
>
> dr-x------ 2 myuser myuser 0 Dec 10 10:02 *.*
>
> dr-xr-xr-x 9 myuser myuser 0 Dec 10 10:02 *..*
>
> lrwx------ 1 myuser myuser 64 Dec 10 10:02 *0* -> /dev/pts/8
>
> lrwx------ 1 myuser myuser 64 Dec 10 10:02 *1* -> /dev/pts/8
>
> lrwx------ 1 myuser myuser 64 Dec 10 10:02 *10* ->
> 'anon_inode:[eventpoll]'
>
> ...
>
> lrwx------ 1 myuser myuser 64 Dec 10 10:02 *8* ->
> '/mnt/b/data/logs/my.binarylog.host (deleted)' ## << how to detect this?
>
> ...
>
> myuser*@*host* /proc/94913/fd $* *mount|grep mnt/b*
>
> /dev/sdb on /*mnt/b* type xfs
> (rw,relatime,attr2,inode64,logbufs=8,logbsize=32k,noquota)
>
> myuser*@*host* /proc/94913/fd $* *uname -a*
>
> Linux host 5.4.0-126-generic #142~18.04.1-Ubuntu SMP Thu Sep 1 16:25:16
> UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
>
> myuser*@*host* /proc/94913/fd $* *cat /etc/lsb-release *
>
> DISTRIB_ID=Ubuntu
>
> DISTRIB_RELEASE=18.04
>
> DISTRIB_CODENAME=bionic
>
> DISTRIB_DESCRIPTION="Ubuntu 18.04.5 LTS"
>
> myuser*@*host* /proc/94913/fd $*
>
> ~~~
>
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