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MQSeries.net Forum IndexGeneral IBM MQ Supportmq error log rotation

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tczielke
PostPosted: Sat Mar 17, 2018 5:27 am Post subject: Reply with quote

Shaman

Joined: 08 Jul 2010
Posts: 749
Location: Illinois, USA

rekarm01 added some helpful information from the manual on how this works and how it changed at 9.0.4. I wanted to also just highlight the following for Linux/Unix.

1) On Linux (probably most other Unix systems, too) a file is identified by its inode, not its hard link. A name like /var/mqm/qmgrs/QM1/errors/AMQERR01.LOG is really a hard link to that inode, and is not what uniquely identifies the file. You can have multiple hard links to the same inode. So it is possible to have two hard links AMQERR01.LOG and MONKEY both pointing to the same inode 1234 and 1234 is what really truly identifies the file, not AMQERR01.LOG. If you do writes to both the hard links of AMQERR01.LOG and MONKEY, they both get written to the inode 1234.

2) A file will not be removed by Linux (and probably other Unix systems, too) until all hard links are removed to the inode AND no processes have that inode open. This is one reason why the rm (remove) command is called rm and not del. You are not deleting a file when you run the rm command. You are removing a hard link to the inode. Let's say there is only one hard link (e.g. AMQERR01.LOG) to the inode 1234. You can do a "rm AMQERR01.LOG" and remove the hard link, but as long as a process has inode 1234 open, that inode will never be deleted by the operating system.

You need to take the above into consideration when desigining any application to read the AMQ error logs. With the 9.0.4 approach, it sounds like you could get yourself into a situation where a long running process that is reading the AMQ error logs could prevent the underlying file inode for AMQERR03.LOG from being deleted by the operating system, if you are not careful with your design.
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Andyh
PostPosted: Sun Mar 18, 2018 12:44 pm Post subject: Reply with quote

Disciple

Joined: 29 Jul 2010
Posts: 158

The mechanism used by the distributed code base to rotate the error log files changed in V9.0.4, to a more standard 'rename' style implementation. This was partly to support 3rd party tools that were assuming this style of rollover.

MQ 9.0.5 makes further, more significant, changes to the error log capabilities,
see https://www.ibm.com/support/knowledgecenter/SSFKSJ_9.0.0/com.ibm.mq.con.doc/q019020_.htm for more detail.
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rekarm01
PostPosted: Wed Mar 21, 2018 2:22 pm Post subject: Reply with quote

Grand Master

Joined: 25 Jun 2008
Posts: 1322

crashdog wrote:
The knowledge center was the first place that I checked, ... But the KC does not describe anything on how the error log files are rotated.

Re-read my previous post. The links I provided seemed to describe in detail how MQ rotates log files. What's missing?
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