update.sh

#!/bin/sh
# https://github.com/nakamochi/sysupdates
# pull changes from a remote git repo and run the "apply" script.
# commits are expected to be signed by gpg keys with a sufficient
# trust level to satisfy git pull --verify-signatures.
# the script is expected to be run as root, to allow making changes to the
# operating system.
# in the future, the plan is to provide an on-screen git diff and apply updates
# after user confirmation.

# git branch to pull from. defaults to master.
# another value is "dev", for a development aka unstable version.
BRANCH="${1:-master}"
# output everything to a temp file and print its contents only in case of an error,
# so that when run via a cronjob, the output is empty on success which prevents
# needless emails, were any configured.
LOGFILE="${LOGFILE:-/var/log/sysupdate.log}"
# a local git repo dir where to pull the updates into.
REPODIR="${REPODIR:-/ssd/sysupdates}"

# multiple running instances of the script would certainly result in race conditions.
# so, we serialize runs using a lock file, timing out with an error after 15min.
if [ -z "$NAKAMOCHI_SYSUPDATE_LOCK" ]; then
    # use the script itself as the lock file
    lockfile=$0
    exec env NAKAMOCHI_SYSUPDATE_LOCK=1 \
      flock --exclusive --timeout 900 "$lockfile" "$0" "$@"
fi

# start of the sysupdate; trim prevously logged runs
date > $LOGFILE

# fetch updates from remote
cd "$REPODIR"
{
git remote set-url origin https://github.com/nakamochi/sysupdates.git
git fetch origin             # in case the refspec is unknown locally yet
git reset --hard HEAD        # remove local changes
git clean -fd                # force-delete untracked files
git checkout "$BRANCH"
git pull --verify-signatures
} >> $LOGFILE 2>&1
if [ $? -ne 0 ]; then
    echo "ERROR: git pull failed"
    cat $LOGFILE
    exit 1
fi

# run repo's update script
export SYSUPDATES_ROOTDIR="$REPODIR"
export SYSUPDATES_CHANNEL="$BRANCH"
./apply.sh >> $LOGFILE 2>&1
if [ $? -ne 0 ]; then
    echo "ERROR: apply failed"
    cat $LOGFILE
    exit 1
fi