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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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logger(1B)					     SunOS/BSD Compatibility Package Commands						logger(1B)

NAME
logger - add entries to the system log SYNOPSIS
/usr/ucb/logger [-f filename] [-i] [-p priority] [-t tag] mm [message]... DESCRIPTION
The logger utility provides a method for adding one-line entries to the system log file from the command line. One or more message argu- ments can be given on the command line, in which case each is logged immediately. If message is unspecified, either the file indicated with -f or the standard input is added to the log. Otherwise, a filename can be specified, in which case each line in the file is logged. If neither is specified, logger reads and logs messages on a line-by-line basis from the standard input. OPTIONS
The following options are supported: -i Log the process ID of the logger process with each line. -f filename Use the contents of filename as the message to log. -p priority Enter the message with the specified priority. The message priority can be specified numerically, or as a facility.level pair. For example, `-p local3.info' assigns the message priority to the info level in the local3 facility. The default pri- ority is user.notice. -t tag Mark each line added to the log with the specified tag. EXAMPLES
Example 1: Logging a message The command: example% logger System rebooted will log the message `System rebooted' to the facility at priority notice to be treated by syslogd as other messages to the facility notice are. Example 2: Logging messages from a file The command: example% logger -p local0.notice -t HOSTIDM -f /dev/idmc will read from the file /dev/idmc and will log each line in that file as a message with the tag `HOSTIDM' at priority notice to be treated by syslogd as other messages to the facility local0 are. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscpu | +-----------------------------+-----------------------------+ SEE ALSO
syslogd(1M), syslog(3C), attributes(5) SunOS 5.10 14 Sep 1992 logger(1B)
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