Tag Archives: nfs

NFS automount evolves

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I’ve updated the NFS automount script that provides “self-healing” NFS mounts. The script now allows a mount to be defined as read-write or read-only, and then subsequently monitors that the share is mounted as R/W or R/O (of course, it can’t mount a share that has been shared as R/O as R/W). Both Linux (tested on CentOS 6.1) and FreeBSD versions are provided.

Since various systems can provide cross-mounts via NFS, and they may be started/rebooted at the same time, various shares may or may not be available at each system’s boot time. By utilizing this script the mounts become available soon after the respective share becomes available (simply adjust the run frequency in crontab to the needs of your specific application). Also, by not adding the NFS mount points in fstab the boot process is not delayed by a share that is not [yet] available.

First for CentOS/Linux:

#!/bin/sh

SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin

# set mount/remount request flags
mount=false
remount=false

# remote system name
remotesystem="$1"

# rw/ro
if [ "$2" = "rw" ]; then
    mountmode="-w"
else
    mountmode="-r"
fi

# remote share name
remoteshare="$3"

# local mount point
mountpoint="$4"

# file to indicate local mount status
testfile=${mountpoint}/"$5" 

# rw test file
rw_testfile=${mountpoint}/nfs_enforcer_rw_testfile

# command locations
pingcmd=/bin/ping
showmountcmd=/usr/sbin/showmount
grepcmd=/bin/grep
mountcmd=/bin/mount
umountcmd=/bin/umount
statcmd=/usr/bin/stat
touchcmd=/bin/touch
rmcmd=/bin/rm

# --- end variables ---

# make sure the mountpoint is not stale
statresult=`${statcmd} ${mountpoint} 2>&1 | ${grepcmd} "Stale"`

if [ "${statresult}" != "" ]; then
   #result not empty: mountpoint is stale; remove it
   ${umountcmd} -f ${mountpoint}
fi

# ping the remote system (2 sec timeout)
${pingcmd} -w2 -c1 -q ${remotesystem} > /dev/null 2>&1

# make sure the remote system is reachable
if [ "$?" -eq "0" ]; then

   # query the availability of the remote share; not empty result indicates OK
   offsiteshare=`${showmountcmd} -e ${remotesystem} | ${grepcmd} "${remoteshare}"`
   if [ "${offsiteshare}" != "" ] ; then

      # make sure the local mount point (directory) exists (so that [re-]mount, if necessary, is valid)
      if [ -d ${mountpoint} ] ; then

         localmount=`${mountcmd} | ${grepcmd} "${mountpoint}"`

         # make sure the share test file is _not_ present (to make sure the mountpoint is inactive)
         if [ ! -f ${testfile} ] ; then

            # make sure the local mountpoint is inactive (double checking)
            if [ "${localmount}" = "" ] ; then

               # all set to go; request mount
               mount=true
            fi

         else 

            # make sure the local mountpoint is active (double checking)
            if [ "${localmount}" != "" ] ; then

               # attempt to create a test file..
               ${touchcmd} ${rw_testfile} > /dev/null  2>&1

               # ..and test its existence; first handle RW mounted shares:
               if [ -f ${rw_testfile} ] ; then

                  # share was RO requested
                  if [ "$2" = "ro" ]; then
                     remount=true
                  fi

                  # Delete the testfile
                  ${rmcmd} ${rw_testfile}

               # hanle RO mounted shares:
               else

                  # share was RW requested
                  if [ "$2" = "rw" ]; then
                     remount=true
                  fi
               fi
            fi
         fi
      fi
   fi
fi

# perform remount (unmount, request mount)
if $remount ; then
   ${umountcmd} -f ${mountpoint}
   mount=true
fi

# perform mount when so requested
if $mount ; then
   ${mountcmd} ${mountmode} -t nfs ${remotesystem}:${remoteshare} ${mountpoint}
fi

exit 0

Then for FreeBSD/UNIX:

#!/bin/sh

SHELL=/bin/sh
PATH=/etc:/bin:/sbin:/bin:/usr/bin:/usr/sbin:/usr/local/bin

# set mount/remount request flags
mount=false
remount=false

# remote system name
remotesystem="$1"

# rw/ro
if [ "$2" = "rw" ]; then
    mountmode="-w"
else
    mountmode="-r"
fi

# remote share name
remoteshare="$3"

# local mount point
mountpoint="$4"

# file to indicate local mount status
testfile=${mountpoint}/"$5" 

# rw test file
rw_testfile=${mountpoint}/nfs_enforcer_rw_testfile

# command locations
pingcmd=/sbin/ping
showmountcmd=/usr/bin/showmount
grepcmd=/usr/bin/grep
mountcmd=/sbin/mount
umountcmd=/sbin/umount
statcmd=stat
touchcmd=/usr/bin/touch
rmcmd=/bin/rm

# --- end variables ---

# make sure the mountpoint is not stale
statresult=`${statcmd} ${mountpoint} 2>&1 | ${grepcmd} "Stale"`

if [ "${statresult}" != "" ]; then
   #result not empty: mountpoint is stale; remove it
   ${umountcmd} -f ${mountpoint}
fi

# ping the remote system (2 sec timeout)
remoteping=`${pingcmd} -c1 -o -q -t2 ${remotesystem} | grep " 0.0%"`

# make sure the remote system is reachable
if [ "${remoteping}" != "" ] ; then

   # query the availability of the remote share; not empty result indicates OK
   offsiteshare=`${showmountcmd} -e ${remotesystem} | ${grepcmd} "${remoteshare}"`
   if [ "${offsiteshare}" != "" ] ; then

      # make sure the local mount point (directory) exists (so that [re-]mount, if necessary, is valid)
      if [ -d ${mountpoint} ] ; then

         localmount=`${mountcmd} | ${grepcmd} "${mountpoint}"`

         # make sure the share test file is _not_ present (to make sure the mountpoint is inactive)
         if [ ! -f ${testfile} ] ; then

            # make sure the local mountpoint is inactive (double checking)
            if [ "${localmount}" = "" ] ; then

               # all set to go; request mount
               mount=true
            fi

         else

            # make sure the local mountpoint is active (double checking)
            if [ "${localmount}" != "" ] ; then

               # attempt to create a test file..
               ${touchcmd} ${rw_testfile} > /dev/null  2>&1

               # ..and test its existence; first handle RW mounted shares:
               if [ -f ${rw_testfile} ] ; then

                  # share was RO requested
                  if [ "$2" = "ro" ]; then
                     remount=true
                  fi

                  # Delete the testfile
                  ${rmcmd} ${rw_testfile}

               # hanle RO mounted shares:
               else

                  # share was RW requested
                  if [ "$2" = "rw" ]; then
                     remount=true
                  fi
               fi
            fi
         fi
      fi
   fi
fi

# perform remount (unmount, request mount)
if $remount ; then
   ${umountcmd} -f ${mountpoint}
   mount=true
fi

# perform mount when so requested
if $mount ; then
   ${mountcmd} ${mountmode} -t nfs ${remotesystem}:${remoteshare} ${mountpoint}
fi

exit 0

You should run the automount script from a runfile, like so:

#!/bin/sh

NFS_ENFORCE=/usr/local/sbin/nfs_enforcer

# Separate the following parameters with spaces:
#
# - nfs enforcer command (set above)
# - remote system name (must be resolvable)
# - read/write (rw) or read-only (ro); NOTE: share may be read-only regardless of how this is set
# - remote share name (from remote's /etc/exports)
# - local mount point (existing local directory)
# - share test file (an immutable file on the share)

# e.g.
# $NFS_ENFORCE dbsysvm rw /nfs4shares/conduit /mnt/dbsys_conduit .conduit@dbsysvm
# or (for local remount read-only)
# $NFS_ENFORCE localhost ro /var/web/projects/repository /mnt/rorepo .repository@localhost

$NFS_ENFORCE localhost ro /var/web/projects/repository /mnt/rorepo .repository@localhost

exit 0

..and call the the above runfile from crontab:

*/10  *  *  *  *  root  /usr/local/sbin/nfs_enforcer.batch > /dev/null

NFS automount, Linux (CentOS) version

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Last summer I posted a script that would repeatedly (via cron) check on a availability and status of a NFS mount, and attempt to keep it mounted if possible. That script was written for (Free)BSD. Below is a slightly modified version that runs on Linux (in this case, CentOS).

#!/bin/sh

SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin

# remote system name
remotesystem=sunrise.externalized.net

# remote share name
remoteshare=/nfs4exports/minecraft-backups

# local mount point
mountpoint=/bak/remote

# file to indicate local mount status
testfile=$mountpoint/.minecraftbackups

# command locations
pingcmd=/bin/ping
showmountcmd=/usr/sbin/showmount
grepcmd=/bin/grep
mountcmd=/bin/mount
umountcmd=/bin/umount
statcmd=/usr/bin/stat

# --- end variables ---

# make sure the mountpoint is not stale
testvar=`${statcmd} ${mountpoint} 2>&1 | ${grepcmd} "Stale"`

if [ "${testvar}" != "" ]; then
   #result not empty: mountpoint is stale; remove it
   ${umountcmd} -f ${mountpoint}
fi

# ping the remote system (2 sec timeout)
${pingcmd} -w2 -c1 -q ${remotesystem} > /dev/null 2>&1

if [ "$?" -eq "0" ]; then

   # server is available so query availability of the remote share; not empty is OK
   offsiteshare=`${showmountcmd} -e ${remotesystem} | ${grepcmd} "${remoteshare}"`

   # make sure the local mountpoint is not active
   localmount=`${mountcmd} | ${grepcmd} "${mountpoint}"`

   if [ "${offsiteshare}" != "" ] ; then
      if [ ! -e ${testfile} ] ; then
         if [ "${localmount}" = "" ] ; then
            ${mountcmd} -w -t nfs ${remotesystem}:${remoteshare} ${mountpoint}
         fi
      fi
   fi
fi

exit 0

Mounting an NFS share after boot, and checking up on it periodically…

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I needed to automatically mount an NFS share after reboot. But the availability of that share could not be guaranteed – the system on the LAN offering the share might be down for maintenance when the system mounting the share is being rebooted. In such case there would be a lengthy wait during the boot sequence until the mount attempt would time out.

So I wrote a short script to handle the situation. When initialized at boot time through init.d or rc.d, it’ll first attempt to mount the share, but then times out in two seconds (this is a LAN NFS share so if the system offering the share is up there should not be a longer delay than that) and so the boot sequence is not slowed down terribly. (see update below) Once boot is complete, the script is run via cron every five minutes. Depending on the criticality of the share you may want to make that time shorter or longer. In this case it is a backup share which is not critical for the system’s functioning.

This technique would handle circular mounts, too, but obviously you would run into trouble if the mounts are required for successful system boot.

For this to work successfully add a marker file, such as “.myremoteservertransfers” in my example script below, in the share folder on the system exporting the share. I usually set the undeletable attribute on the file to make sure it doesn’t get accidentally deleted.

Update: Even with this code the boot sequence appears to hang until portmap times out (which takes quite a while) if the NFS share is not available at boot time. I removed the rc.d mount attempt and just shortened the cron poll period to 1 minute. That way the share will be up very quickly once it becomes available, yet the overhead caused by the periodic ping is minimal (both servers are on local LAN).

#!/bin/sh

SHELL=/bin/sh
PATH=/etc:/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin

# remote system name
remotesystem=myremoteserver

# remote share name
remoteshare=/nfsexports/backupshare

# local mount point
mountpoint=/localbackups/TRANSFERS/${myremoteserver}

# file to indicate local mount status
testfile=$mountpoint/.myremoteservertransfers

# --- end variables ---

# ping result to the remote system (2 sec timeout); not empty is OK
remoteping=`ping -c1 -o -q -t2 ${remotesystem} | grep " 0.0%"`

if [ "${remoteping}" != "" ] ; then

   # server is available so query availability of the remote share; not empty is OK
   offsiteshare=`showmount -e ${remotesystem} | grep "${remoteshare}"`

   # make sure the local mountpoint is not active; not empty is OK
   localmount=`/sbin/mount | /usr/bin/grep "${mountpoint}"`

   if [ "${offsiteshare}" != "" ] ; then
      if [ ! -e ${testfile} ] ; then
         if [ "${localmount}" = "" ] ; then
            mount -r -t nfs ${remotesystem}:${remoteshare} ${mountpoint}
         fi
      fi
   fi
fi

exit 0