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Full Discussion: bash: closing file descriptors from a process
Top Forums Shell Programming and Scripting bash: closing file descriptors from a process Post 302452604 by jelloir on Sunday 12th of September 2010 04:12:21 AM
Old 09-12-2010
bash: closing file descriptors from a process
Below is a test script to illustrate a problem from a larger script I am writing.

Code:
$ cat /tmp/loggingtest 
#!/bin/bash

lvcreate -s -l 100%FREE -n var-data-snapshot vg00/var-data 2> >(logger -t "loggingtest.crit") 1> >(logger -t "loggingtest.info")

sync &
wait

lvremove -f vg00/var-data-snapshot 2> >(logger -t "loggingtest.crit") 1> >(logger -t "loggingtest.info")

When I run this I receive the following output in /var/log/syslog.
Specifically I cannot understand where the "File descriptor 62 left open" and "File descriptor 63 left open" errors are coming from. Also the script hangs until I press enter.

Code:
Sep 12 11:57:39 debvelopment loggingtest.crit: File descriptor 62 left open
Sep 12 11:57:39 debvelopment loggingtest.crit: File descriptor 63 left open
Sep 12 11:57:39 debvelopment loggingtest.info:   Logical volume "var-data-snapshot" created
Sep 12 11:57:39 debvelopment loggingtest.crit: File descriptor 62 left open
Sep 12 11:57:39 debvelopment loggingtest.crit: File descriptor 63 left open
Sep 12 11:57:39 debvelopment loggingtest.info:   Logical volume "var-data-snapshot" successfully removed

I have done research but I am finding it difficult to understand whether these errors are related to lvm, syslog or something I am doing wrong in bash? let alone how to close the file descriptors properly.

---------- Post updated at 06:12 PM ---------- Previous update was at 12:01 PM ----------

I can now prevent the errors and know that the descriptors are from "logger" but I still do not understand it.

I added "62>&- 63>&-" to the end of each command and this resolves the errors e.g.

Code:
#!/bin/bash

lvcreate -s -l 100%FREE -n var-data-snapshot vg00/var-data 2> >(logger -t "loggingtest.crit") 1> >(logger -t "loggingtest.info") 62>&- 63>&-

sync &
wait

lvremove -f vg00/var-data-snapshot 2> >(logger -t "loggingtest.crit") 1> >(logger -t "loggingtest.info") 62>&- 63>&-

But what if the file descriptors where to change? How can I identify the relevant file descriptors and then close them? Do I need to even be concerned as they appear to close anyway?

Thanks
 

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LEARN ABOUT DEBIAN

lvremove

LVREMOVE(8)						      System Manager's Manual						       LVREMOVE(8)

NAME

       lvremove - remove a logical volume

SYNOPSIS

       lvremove  [-A|--autobackup  {y|n}]  [-d|--debug] [-h|--help] [-t|--test] [-v|--verbose] [--version] [-f|--force] [--noudevsync] LogicalVol-
       ume{Name|Path} [LogicalVolume{Name|Path}...]

DESCRIPTION

       lvremove removes one or more logical volumes.  Confirmation will be requested before  deactivating  any	active	logical  volume  prior	to
       removal.   Logical  volumes  cannot be deactivated or removed while they are open (e.g. if they contain a mounted filesystem).  Removing an
       origin logical volume will also remove all dependent snapshots.

       If the logical volume is clustered then it must be deactivated on all nodes in the cluster before it can be removed. A single lvchange com-
       mand issued from one node can do this.

OPTIONS

       See lvm(8) for common options.

       -f, --force
	      Remove active logical volumes without confirmation.

       --noudevsync
	      Disable  udev  synchronisation. The process will not wait for notification from udev.  It will continue irrespective of any possible
	      udev processing in the background.  You should only use this if udev is not running or has rules that ignore the devices	LVM2  cre-
	      ates.

EXAMPLES

       Remove the active logical volume lvol1 in volume group vg00 without asking for confirmation:

       lvremove -f vg00/lvol1

       Remove all logical volumes in volume group vg00:

       lvremove vg00

SEE ALSO

       lvcreate(8), lvdisplay(8), lvchange(8), lvm(8), lvs(8), lvscan(8), vgremove(8)

Sistina Software UK					 LVM TOOLS 2.02.95(2) (2012-03-06)					       LVREMOVE(8)
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