Exploring NFS file locking

nfs-locking.md

Pre-requisites

• NFSv4
• Have all_squash in /etc/exports, like so:

/opt/vmlocks 10.0.1.38(rw,sync,all_squash) 10.0.1.244(rw,sync,all_squash)

Testing

• Mount /opt/vmlocks under /mnt (lock option should be there by default)
• Copy t.sh contents (see below)
• Copy runner.sh contents (see below)
• Run test sequence in different machines:

echo {1..50} | xargs -n 1 -P 2 flock -o /mnt/a ./t.sh

• Keep it running for some time

Notes

• There is a certain delay before a remote senses file unlocking by another machine

runner.sh

#!/bin/bash

PARALLEL=$1
TOTAL=$2

for I in $(seq ${TOTAL})
do
    for J in $(seq ${PARALLEL})
    do
        echo ${I}_${J}
    done | xargs -n 1 -P ${PARALLEL} flock -o /mnt/a ssh ${SSH_LOGIN} nfs-locking/t.sh
    sleep $(printf "0.%03d\n" $(shuf -i 1-999 -n 1))
done

t.sh

#!/bin/bash

set -e

RESOURCE=/tmp/resource

[ -f "${RESOURCE}" ] && echo FAILURE $1 && exit 1
date >"${RESOURCE}"
sleep 0.1
rm "${RESOURCE}"
echo SUCCESS $1 1>&2