Run a bash script or cronjob with a lockfile and timeout

This is a pretty old post (published on September 15, 2014). Therefore the contents may be outdated and only useful for archiving purposes.
readonly PROGNAME=$(basename "$0")
readonly LOCKFILE_DIR=/tmp
readonly LOCK_FD=200
lock() {
    local prefix=$1
    local fd=${2:-$LOCK_FD}
    local lock_file=$LOCKFILE_DIR/$prefix.lock
    # create lock file
    eval "exec $fd>$lock_file"
    # acquier the lock
    flock -n $fd \
        && return 0 \
        || return 1
eexit() {
    local error_str="$@"
    echo $error_str
    exit 1
main() {
    lock $PROGNAME \
        || eexit "Only one instance of $PROGNAME can run at one time."
    timeout 5 /var/www/crontest/
main >> /var/www/crontest/log

Inspired by Kfir Lavi

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