S/390 NFS Post Box for remote hosts (postbox)

• Introduction
• Remote Host Setup
• NFS Server Setup
• Sample NFS Server - scripts to be executed on remote hosts
• Sample NFS Server - admin scripts

Introduction

Often, you need to update files or execute commands on some or all of your Linux hosts. For example, you need to shutdown all your hosts for routine hardware or software maintenance. Or you may want to update some file, such as /etc/motd, on all or some of hosts. However, this can be time consuming and error prone if you have many of these hosts when you are using telnet or ftp.Using an NFS server, you can set up a simple postbox system to issue the necessary commands automatically on all or only certain hosts. The postbox can be scanned periodically using a crontab on the remote hosts to look for commands to execute.

This technique consists of the following parts:

• A common NFS server with a postbox directory and a postbox file for each host
  • The postbox files are created, modified, or deleted as necessary by the administrator
• A bash script on each host to check the postbox for the host
  • If the postbox entry for the host on the NFS server is present, execute the postbox entry, then remove the file from the server
  • If there is no postbox entry for the host, no action is taken.
• A cron task to execute the bash script on each host at predetermined intervals.

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Remote Host Setup

On each remote host you want to participate, you set up a remote postbox, insert a script to check the postbox, and then a crontab entry to periodically check the NFS postbox.

1. mkdir /home2/postbox (Our convention is to put all user directories on a separate volume from the root and mount it as /home2 so we can ipl various root volumes without having to recreate the user files).
2. mkdir /home2/postbox/bin
3. Create the script to check the NFS postbox

   /home2/postbox/bin/admin.check.postbox

   #.............................................................................. # check $adminBOX file for bash scripts to execute # - all hosts execute file adminall on the NFS server # - $HOSTNAME executes file $HOSTNAME on the NFS server, then removes the file #.............................................................................. PATH=$PATH:/sbin:/usr/sbin adminBOX=/mnt/admin/postbox HOSTBOX=/home2/admin/postbox # test ! -d "$adminBOX" -a "$HOSTNAME" != "syssbld" && \      mkdir -p /mnt/admin && \      mount -t NFS -o rw,timeo=300,retrans=5,wsize=8192,rsize=8192,hard,intr,bg,suid,nolock                  NFSserverIP:/mnt/admin /mnt/admin # test -f "$adminBOX/adminall" && \ bash $adminBOX/adminall # test -f "$adminBOX/$HOSTNAME" && \      bash $adminBOX/$HOSTNAME && \      rm $adminBOX/$HOSTNAME # sleep 1 case $HOSTNAME in      syssbld      # do not dismount postbox on NFS server host      ;;      sysstst)      # do not dismount postbox on certain other hosts      ;;      *)      umount -f /mnt/admin      ;; esac

4. Create the crontab entry - generally, we check once a day, during third shift. Each host has a slightly different time to check to minimize clustering on activity on the net and NFS server.

   # check at 1:36 a.m. every day for this remote host 36 1 * * * /bin/bash   /home2/admin/postbox/bin/admin.check.postbox

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NFS Postbox Server Setup

1. Set up your /etc/exports file to allow read/write to your postbox directory. If you do not allow write, the remote host will execute the file each time the cron interval is executed. To avoid this, allow the file to be removed from the NFS server by the remote host. I've used the "net ip/subnet mask" format.

   /mnt/admin/postbox 10.1.1.64/255.255.255.192(rw,no_root_squash)

2. mkdir /mnt/admin/postbox
   • The file names in the postbox are the hostnames for each host that you want to transmit a bash script to. Each bash script could be the same of different. For illustrative purposes, I am going to assume that I have 3 hosts (syslnx1, syslnx2, and syslnx3)
   • /mnt/admin/postbox - postbox on local NFS server. Each remote host may have a file in it to be acted upon.
     • file name "adminall" - executed by all remote host, not deleted
     • file name "hostname" - executed by remote host, then deleted
3. mkdir /mnt/admin/postbox/sample - files to help generate remote host scripts

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Sample NFS scripts and files to be sent to/ execute on remote host

These are some of the things that you might want to do on the remote host. They are kept in "/mnt/admin/postbox/sample".

• Copy files to remote host
• Execute commands at remote host
• Execute command at remote host at a later time
• Message to be issued on remote host
• Shutdown on Sunday on remote host

Note that "#!/bin/bash" is not present in the scripts to be executed by the remote hosts because they are executed using "/bin/bash scriptname" on the remote hosts.They are set up so that they can be concatenated to other scripts in the postbox for a remote host, preserving any pending scripts.

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Copy files to remote host

back to remote scripts

Execute commands at remote host

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Execute command at remote host at a later time

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Message to be issued on remote host

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Shutdown on Sunday on remote host

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Sample NFS Server - administrative scripts

• Generate scripts in postbox for each remote host
• Modify the Sunday Shutdown Script for a different time and day
• Delete "at" commands

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Generate scripts in postbox for each remote host

This examples takes scripts that have been built and propagates them to the /mnt/admin/postbox directory, one file per host. To preserve any previous pending scripts that have not been read, the results of this execution are appended to the pending files.

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Modify a script for date and time

This example takes the /mnt/admin/postbox/sample/remote.shut.sunday file and modifies for a 2nd shift shutdown (2:00 p.m.). The results are stored in /mnt/admin/postbox/sample/temp.shut.2nd.xxxx where xxxx is the date argument given to the script.

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Delete "at" commands

Sometimes you may have to delete some of the "at" commands already issued. For safety sake, you probably will have to logon to each host you need to delete and check their pending "at" commands ("atq'). Then you can use the admin.atqdel script to delete a range of "at" commands.

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