[systemd-devel] Netconsole NG

["Jóhann B. Guðmundsson"]

On 04/08/2014 12:10 PM, poma wrote:
> [Service]
> EnvironmentFile=/etc/sysconfig/netconsole-zbyszek
> RemainAfterExit=yes
> ExecStart=/sbin/modprobe netconsole netconsole=@/${SRC_DEV},@${DST_IP}/
> ExecStop=/sbin/modprobe -r netconsole

On popular demand of me providing more detailed criticism than just 
"this is rubbish" as well as I got somewhat myself to blame for poorly 
written unit files given that the best practical of unit writing resides 
in my head by the experience of migrating so many legacy sysv initscript 
to native systemd units and driven half way to insanity while doing so.

So let me clarify why I think this is rubbish.

For the first you are using the wrong Type for that unit file as in the 
build in default which is Type=simple for the purpose of this unit along 
with RemainAfterExit=yes in it when you should be using Type=oneshot unit

Secondly let me start with "EnvironmentFile=" in 99.9% times this is 
entirely unnecessary since what is contains within those environment 
files are configuration changes to daemon startup for daemons that are 
so poorly written they dont support reading configuration files on startup.

Now on the 21 century within the systemd universe, administrators are ( 
supposted to be ) using drop in configuration snippets that contain that 
administrator overwrite to overcome that daemons lack of reading 
configuration file in the relvant unit's .d configuration directory that 
resides under /etc/systemd/systemd/ or better yet developers that 
maintain and own that component should be rewriting it's daemon to 
support parsing configuration file(s) at startup.

If you happen to be using the 00.1% components that actually has valid 
usecase for using "EnvironmentFile=" definition in type service units 
these days, then those environment files should reside in a components 
.d directory under /etc to make them cross distributional not under 
/etc/sysconfig or under /etc/default and hopefully one day I will have 
manage to remove all traces and usages of environmental files in 
/etc/sysconfig in Fedora ( but achieving that is more like David vs 
Goliath or Jóhann vs Red Hat.) as well as others doing the same in their 
distribution of choice

Thirdly under no circumstances and I mean NEVER should you be loading 
and unloading modules from within a systemd unit YES NEVER!!!

If you need for one reason or another to load module you do so by 
placing .conf configuration snippet in /etc/modules-load.d which tell 
the system which kernel modules to load but fact is if you actually need 
to load some module manually like this something is wrong since modules 
should be automatic loaded by PCI IDs, USB IDs, DMI IDs or similar 
triggers encoded in the kernel modules themselves these days.

And you place .conf configuration snippet in /etc/modprobe.d which 
contains which parameters the kernel module uses when loading.

Which leads to that service section being rubbish as well as the 
existence of that entire unit being o_O since the correct way ( always ) 
when dealing with module and their option is what I described here above 
which leads to for netconsole being....

/etc/modules-load.d/netconsole.conf
# Load netconsole.ko at boot
netconsole

And

/etc/modprobe.d/netconsole.conf
# load netconsole options
options netconsole netconsole=@192.168.1.2/enp1s2, at 192.168.1.1/

And since you are using netconsole you probably want to increase the 
logvel as well

/etc/sysctl.d/10-netconsole.conf
#raising loglevel from 7 to 8
kernel.printk = 8 4 1 7

JBG