Print to the console from hook script

RohitRC · May 2, 2022, 9:00am

Is it possible to print to the console from a snap hook without including exit 1? I want to print few warning messages from configure hook.

ogra · May 2, 2022, 9:36am

no, it is not, but you can use logger -t $SNAP "$MESSAGE" from inside your hook to write to the journal though …

RohitRC · May 2, 2022, 12:35pm

Hello I followed your method and included the logger command in configure hook. During installation of my snap, the configure hook get executed. My service has install-mode disabled. I am running the following journalctl command in host system.

sudo journalctl -r -u snap.<snapname>.<servicename>

But I can’t see any warning messages getting printed after installation.

ogra · May 2, 2022, 12:40pm

ah, sorry, it should have been logger -t $SNAP_NAME ...

here is an example where i make pretty excessive use of it in the install hook:

github.com

ogra1/rak-pktfwd-snap/blob/main/snap/hooks/install

#! /bin/sh

# copy default config to writable place if it does not exist yet
# note that we default to EU 86x
if [ ! -e $SNAP_COMMON/global_conf.json ]; then
  cp $SNAP/etc/global_conf.eu_863_870.json $SNAP_COMMON/global_conf.json
fi

# only start if all interfaces are connected
DISABLED=""

disable(){
  snapctl stop --disable ${SNAP_NAME}.pktfwd
}

if ! snapctl is-connected gpio; then
  logger -t ${SNAP_NAME} "need access to gpio !!!"
  logger -t ${SNAP_NAME} "please run snap connect ${SNAP_NAME}:gpio pi:bcm-gpio-17"
  DISABLED="true"
fi

This file has been truncated. show original

RohitRC · May 2, 2022, 1:15pm

I have fixed the command logger -t ${SNAP_NAME} "warning" but when I run the following journalctl command in host system it doesn’t show the message.

sudo journalctl -r -u snap.<snapname>.<servicename>

I can only find the service logs.

ogra · May 2, 2022, 1:21pm

it will just log under the snap name, not necessarily under the service name …

you could indeed craft the -t option in a way it uses something like snap.${SNAP_NAME}.<servicename> as tag though, but not sure if journald considers it part of the service then …

RohitRC · May 2, 2022, 2:16pm

Found the logs by passing the tag flag while running journalctl.

sudo journalctl -r -t $SNAP_NAME