IV96177: LOGINS HANG TRYING TO WRITE TO UTMP

APAR status

• Closed as program error.

Error description

• The current service packs as of April 2017 contain
  this APAR:
  
  IV91908 REDUCE LOCK CONTENTION ON /ETC/UTMP
  
  The full list of APARs that introduce this issue at
  different levels of AIX is:
  IV90905,IV91372,IV91375,IV91383,IV91375,IV91908,IV92077,
  IV92693
  
  
  After upgrading to a service pack that contains this
  APAR, everything may seem fine at first. There is
  potential, however, that logins will start to hang,
   and can only be cured by a reboot.
  
  
  If you have an open root window at the time, lsof will
  show that something (such as init PID 1)
   is holding a write lock on /etc/utmp, indicated by
  the 'w' in 0uw:
  
  # lsof /etc/utmp
  COMMAND      PID USER   FD   TYPE DEVICE SIZE/OFF NODE
  init           1 root    0uw VREG   10,4   196992  564
  
  NAME
  /etc/utmp
  
  If it is the init process holding the lock, you may also
  see errors on the console or in errpt similar to:
  
  INIT: failed write of utmp entry
  

Local fix

Problem summary

• login sessions start to hang. In customer scenario init
  process while writing to /etc/utmp has taken a write lock
  and it is never released. Hence login sessions hang as they
  do not get lock to write /etc/utmp. This is caused because
  an uninitialized size is assigned to len value in lock
  structure
  

Problem conclusion

• Initialize a size variable to proper value i.e size of lock
  structure before assigning this value to len variable
  in lock structure.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  IV96345 IV96347 IV96348 IV96349 IV96351 IV96352

Fix information

• Fixed component name

  AIX V7.1

• Fixed component ID

  5765H4000

Applicable component levels

• R710 PSY U878629

     UP17/10/30 I 1000