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#!/bin/bash -e
INSTANCE="$1"
if [ -z "$INSTANCE" ]; then
echo "first argument must be the GCE instance (for example, mar280632-365378)"
exit 1
fi
# wait for the instance to exist
until gcloud compute --project=snapd-spread instances describe "$INSTANCE" --zone=us-east1-b >/dev/null 2>&1; do
echo "waiting for instance to exist"
sleep 1
done
OUTPUT_FILE="console-output-$INSTANCE.txt"
backgroundscript=$(mktemp --suffix=.gce-watcher)
cat >> "$backgroundscript" << 'EOF'
INSTANCE="$1"
OUTPUT_FILE="$2"
next=0
truncate -s0 "$OUTPUT_FILE"
while true; do
# The get-serial-port-output command will print on the stdout the new lines
# that the machine emitted on the serial console since the last time it was
# queried. The bookmark is the number ("$next") that we pass with the
# --start parameter; this number is printed by gcloud to the stderr in this
# form:
#
# Specify --start=130061 in the next get-serial-port-output invocation to get only the new output starting from here.
#
# In the subshell below we compute the value of the "$next" variable: we
# store the original stdout into the console-output-bits.txt file, then
# (via a third file descriptor, not to mess with the original stdout) we
# redirect the stderr into the stdout and use "grep" to extract the
# suggested value for the --start parameter.
next=$(
gcloud compute \
--project=snapd-spread \
instances get-serial-port-output "$INSTANCE" \
--start="$next" \
--zone=us-east1-b 3>&1 1>"${OUTPUT_FILE}-bits.txt" 2>&3- | grep -Po -- '--start=\K[0-9]+')
trimmedConsoleSnippet="$(sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//' < ${OUTPUT_FILE}-bits.txt)"
if [ -n "$trimmedConsoleSnippet" ]; then
echo "$trimmedConsoleSnippet" >> "$OUTPUT_FILE"
fi
sleep 1
done
EOF
# start collecting the console output
bash "$backgroundscript" "$INSTANCE" "$OUTPUT_FILE" &
on_exit() {
# Restore the signal handlers to avoid recursion
trap - INT TERM QUIT EXIT
rm -f "$OUTPUT_FILE" "$OUTPUT_FILE-bits.txt"
# kill all processes in this group
kill 0
}
trap "on_exit" INT TERM QUIT EXIT
# wait for it to appear
until [ -f "$OUTPUT_FILE" ]; do
sleep 1
done
# watch it
tail -f "$OUTPUT_FILE"
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