Testing systemctl existence before executing it

[kirawrath]

Since commit c9614c4 kpatch has support for upstart systems,
which means we should test the existence of systemctl before executing
it.

The command command is POSIX compliant, and should be widely
available.

Signed-of-by: Bruno Loreto loretob@amazon.com

[joe-lawrence]

This change makes sense, though make check has a complaint:

$ make check
shellcheck kpatch/kpatch kpatch-build/kpatch-build kpatch-build/kpatch-gcc
In kpatch/kpatch line 472:
	command -v systemctl 2>&1 > /dev/null && systemctl enable kpatch.service
                             ^-- SC2069: The order of the 2>&1 and the redirect matters. The 2>&1 has to be last.
make: *** [check] Error 1
The command "make check" exited with 2.

Maybe command -v systemctl &> /dev/null && systemctl enable kpatch.service would appease shellcheck?

[jpoimboe]

Also is there something we need to do to make sure "kpatch install" actually enables the patch on boot (something similar to kpatch.service) on upstart?

[kirawrath]

Joe: I would love to use &>, however that is a bash-4+ only construct, and looking at the rest of the code, I noticed that only the 2>&1 is employed, so I will keep the same style, using 2>&1, but in the correct order this time.

Josh: For upstart such command is not necessary, simply placing the required files in /etc/init (which is already done) should suffice.

[joe-lawrence]

👍