To test the connection of a server with its time servers (e.g. to check if no firewall is blocking NTP communication), run the following command:

# ntpq -c peers [ip-address-of-timeserver]

If you wish to restrict the maximum number of login sessions for a specific user, you can do this by modifying the .profile of that user:

A=`w| grep $LOGNAME | wc -l`
if [ $A -ge 3 ] ; then
  exit
fi

AIX 5.1 and higher includes a set of System V commands. E.g. the Sun Solaris command "ptree" has been included in AIX as "proctree". Information about all System V commands in AIX can be found in the AIX 5.x differences guides.

This command will show you the process tree of a specific user:

# proctree username

The next part describes a problem where you would want to do a search on a file system to find all directories in it, and to start a backup session per directory found, but not more than 20 backup sessions at once. Usually you would use the "find" command to find those directories, with the "-exec" parameter to execute the backup command. But in this case, it would result in possibly more than 20 active backup sessions at once, which might overload the system.

So, you can create a script that does a "find" and dumps the output to a file first, and then starts reading that file and initiating 20 backups in parallel. But then, the backup can't start, before the "find" command completes, which may take quite a long time, especially if run on a file system with a large number of files. So how do you do "find" commands and backups in parallel? Solve this problem with a pipeline.

Create a pipeline:

# rm -f /tmp/pipe
# mknod /tmp/pipe p

# find [/filesystem] -type d -exec echo {} \; > /tmp/pipe

cat /tmp/pipe | while read entry
do
   # Wait until less than 20 backup sessions are active
   while [ $(jobs -p|wc -l|awk '{print $1}') -ge 20 ]
   do
      sleep 5
   done

   # start backup session in the background
   [backup-command] &
   echo Started backup of $entry at `date`
done
# wait for all backup sessions to end
wait
echo `date`: Backup complete

If you're trying to restoring an mksysb through NIM and constantly get the same error when trying to restore a mksysb on different systems:

0042-006 niminit (To-master) rcmd connection refused

# grep nim /etc/inittab
nim:2:wait:/usr/bin/startsrc -g nim >/dev/console 2>&1

UNIX records its timestamp in seconds since January 1, 1970. An easy way to convert this time stamp to some readable format: unixtimestamp.com.

There's a way to avoid certain entries appearing in the error report indefinitely. You can use this for example for tape cleaning messages:

The following command shows you the entries that are written to the error log, but not reported on:

# errpt -t -F Report=0

# errupdate [Enter]
=D1A1AE6F: [Enter]
Report=False [Enter]
[Ctrl-D]
[Ctrl-D]

Sometimes situations occur where a logical volume is deleted, but the ODM is not up to date. E.g. when "lsvg -l" doesn't show you the logical volume, but the lslv command can still show information about the logical volume. Not good.

To resolve this issue, first try:

# synclvodm -v [volume group name]

# odmget -q name=hd7 CuDv | tee -a /tmp/CuDv.hd7.out
# odmget -q name=hd7 CuAt | tee -a /tmp/CuAt.hd7.out

# odmadd /tmp/[filename]

# odmdelete -o CuDv -q name=hd7
# odmdelete -o CuAt -q name=hd7

Older pSeries systems (Power4) are equipped with environmental sensors. You can read the sensor values using:

# /usr/lpp/diagnostics/bin/uesensor -l

To find the known recommended technology levels:

# oslevel -rq

# oslevel -rl 5300-07

# oslevel -rg 5200-05