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#1
09-12-2010
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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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#2
09-12-2010
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you just have to close them then: Code:
#!/bin/bash
{
exec 62>&-
exec 63>&-
lvcreate -s -l 100%FREE -n var-data-snapshot vg00/var-data
} 2> >(logger -t "loggingtest.crit") 1> >(logger -t "loggingtest.info")
sync &
wait
{
exec 62>&-
exec 63>&-
lvremove -f vg00/var-data-snapshot
} 2> >(logger -t "loggingtest.crit") 1> >(logger -t "loggingtest.info")---------- Post updated at 04:19 PM ---------- Previous update was at 04:16 PM ---------- Thanks to this thread I now know why I have some fds left open even if I close a duplicate fd. |
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| Tags |
| bash, file descriptors, lvm, syslog |
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