Timing issue, installing a package and then modifying one of it's files...

[Adam Morris]

I have come across an unusual timing issue...  I'm not sure what is causing it but it is repeatable...

Here is a single task file from part of my initial set up... (I've removed the AIX and 32 bit variants but they are interspersed with the 64 bit RedHat version.

---

# file: roles/common/tasks/sar.yml

# Ensure that the necessary package is installed on RedHat

- name: ensure that the sysstat package is installed for RedHat based systems

  yum: name="sysstat" state=present

  when: ansible_os_family == "RedHat"

# Add an entry to the cron file to make sure that the line only occurs once

- name: Verify the crontab file is managed by Ansible

  lineinfile: 'backup=no dest=/etc/cron.d/sysstat state=present 

              line="#Ansible: sar" insertbefore="/usr/lib64/sa/sa1"'

  when: ansible_os_family == "RedHat" and ansible_userspace_bits == "64"

# Now modify the cron.d file to check output every ten minutes.

#  cron either has inotify support, or checks certain locations for changes

#  every minute.  Either way, no notification is needed.

- name: modify the cron.d file to run sar every ten minutes for RedHat

  cron: name="sar" backup=no cron_file=sysstat state=present user={{root_user}}

                job="/usr/lib64/sa/sa1 600 1" minute="*/10"

  when: ansible_os_family == "RedHat" and ansible_userspace_bits == "64"

So, when I run this as part of a larger playbook I get the following behaviour (and no errors)

If sysstat is already installed the /etc/cron.d/sysstat file is modified to add the Ansible tag before the existing (default) line and then the cron job is modified to look the way that I want it.  This is what I would expect.

If I run the play again nothing changes.  Again this is what I expect.

If sysstat is not installed then it is installed (as expected) and the sysstat file is modified to add the new cron job.  But the old one is not tagged so I end up with two similar entries in the file.

I could add a deliberate delay in here between installing sysstat and modifying the cron job, but I haven't yet.  I'm wondering why I am seeing the behaviour that I see.

Any thoughts?

Adam

[Michael DeHaan]

Do you think there's a background process spawned by sysstat that is modifying it's own cron job?

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[Adam Morris]

On Tuesday, March 4, 2014 11:04:43 AM UTC-8, Michael DeHaan wrote:

Do you think there's a background process spawned by sysstat that is modifying it's own cron job?

If there is it's fast enough that yum install sysstat && cat /etc/cron.d/sysstat gives me the results that I expect. It looks like the sysstat package includes a default /etc/cron.d/sysstat file that doesn't appear to change at any point.

I'm rather confused by this, unless the install task is returning before it's finished and I don't know why that would happen.

Adam

[Adam Morris]

Running yum manually with rpmverbosity set to debug I can see that the /etc/cron.d/sysstat file is the first one that is deployed from the RPM and the only script appears to be a postinstall script that runs chkconfig. 

I'm trying a run with -vvv and dumping it to a file to see if I can see exactly where the issue lies.  

Adam

[Adam Morris]

My stupidity was at fault...

There is originally a commented out line in the file that ALSO matches the regexp I was using.  So, my change was made to the second of two matching lines and not the first...  Kind of confusing when using insertbefore...

So I have...

example line 1

# line 2 example

and using line in file I insert "#Ansible test" before "line" and it gets put in between lines 1 and 2.  i.e. after line 1 and before line 2.

thus I end up with

example line 1

#Ansible test

# line 2 example

and not 

#Ansible test

example line 1

# line 2 example

as I was expecting...  that behaviour is clearly documented for regexp but it might be worth adding a note to "insertbefore" that it will insert before the LAST line that matches the regexp.

Adam