CentOS 7 should be treated like RHEL 7 in dist/rhel.py

[Lars Kellogg-Stedman]

cloudinit/dists/rhel.py contains the follow code to determine if systemd is in use:

    def uses_systemd(self):
        # Fedora 18 and RHEL 7 were the first adopters in their series
        (dist, vers) = util.system_info()['dist'][:2]
        major = (int)(vers.split('.')[0])
        return ((dist.startswith('Red Hat Enterprise Linux') and major >= 7)
                or (dist.startswith('Fedora') and major >= 18))

This will not produce the correct behavior on CentOS 7, Scientific LInux 7, or any other RHEL-based distribution. Among other issues, this will prevent cloud-init from setting the system hostname correctly. Because these distributions are treated like RHEL6 and earlier, cloud-init writes the persistent hostname into /etc/sysconfig/network, but the hostname is not read from this file when the system boots.

I propose that we replace uses_systemd with the following:

    def uses_systemd(self):
        return os.path.isfile('/usr/bin/systemctl')

[Lars Kellogg-Stedman (larsks)]

The attach patch replaces the distribution-name heuristics in uses_systemd with a check for the systemctl binary.

[Ben Howard (darkmuggle-deactivatedaccount)]

On Fri, Jan 16, 2015 at 09:13:58PM -0000, Lars Kellogg-Stedman wrote:
> The attach patch replaces the distribution-name heuristics in
> uses_systemd with a check for the systemctl binary.
>
> ** Patch added: "0001-fix-check-for-systemd.patch"
> https://bugs.launchpad.net/cloud-init/+bug/1411829/+attachment/4300219/+files/0001-fix-check-for-systemd.patch
>
> --
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> https://bugs.launchpad.net/bugs/1411829
>
> Title:
> CentOS 7 should be treated like RHEL 7 in dist/rhel.py
>
> Status in Init scripts for use on cloud images:
> New
>
> Bug description:
> cloudinit/dists/rhel.py contains the follow code to determine if
> systemd is in use:
>
> def uses_systemd(self):
> # Fedora 18 and RHEL 7 were the first adopters in their series
> (dist, vers) = util.system_info()['dist'][:2]
> major = (int)(vers.split('.')[0])
> return ((dist.startswith('Red Hat Enterprise Linux') and major >= 7)
> or (dist.startswith('Fedora') and major >= 18))
>
>
> This will not produce the correct behavior on CentOS 7, Scientific LInux 7, or any other RHEL-based distribution. Among other issues, this will prevent cloud-init from setting the system hostname correctly. Because these distributions are treated like RHEL6 and earlier, cloud-init writes the persistent hostname into /etc/sysconfig/network, but the hostname is not read from this file when the system boots.
>
> I propose that we replace uses_systemd with the following:
>
> def uses_systemd(self):
> return os.path.isfile('/usr/bin/systemctl')

It might make sense to figure out if systemd is really running. There are
cases where you could have different init systems running:

    def uses_systemd(self):
        return 'systemctl' in os.readlink('/proc/1/exe')

>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/cloud-init/+bug/1411829/+subscriptions
>

[Lars Kellogg-Stedman (larsks)]

I guess the "correct" way of doing it would be to use the "booted" method of "systemd.daemon":

    import systemd.daemon
    if systemd.daemon.booted():
        print 'using systemd'

...which, it turns out, is really just calling lstat("/run/systemd/system"). So I guess that would in fact be the correct test:

    if os.path.isdir('/run/systemd/system'):
        print 'using systemd'

For reference:

https://github.com/systemd/systemd/blob/master/src/libsystemd/sd-daemon/sd-daemon.c#L510

[Lars Kellogg-Stedman (larsks)]

This patch modifies uses_systemd() to mimic the behavior of systemd's own sd_booted() function. This is much more robust than trying to chase distribution/version information.

[Joshua Powers (powersj)]

I believe this should be marked as fixed as the uses_systemd function was updated previous:

https://github.com/cloud-init/cloud-init/blob/master/cloudinit/distros/__init__.py#L100

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2517