db2inst1用户密码自动失效，如何解决？

在AIX5.3操作系统安装了db2V9，使用一段时间发现，db2inst1用户的密码大概1个月就失效一次，输入密码提示
3004-007 You entered an invalid login name or password.
需要使用root用户重新设定密码。

default:
  admin = false
  login = true
  su = true
  daemon = true
  rlogin = true
  sugroups = ALL
  admgroups =
  ttys = ALL
  auth1 = SYSTEM
  auth2 = NONE
  tpath = nosak
  umask = 022
  expires = 0
  SYSTEM = "compat"
  logintimes =
  pwdwarntime = 0
  account_locked = false
  loginretries = 0
  histexpire = 0
  histsize = 0
  minage = 0
  maxage = 0
  maxexpired = -1
  minalpha = 0
  minother = 0
  minlen = 0
  mindiff = 0
  maxrepeats = 8
  dictionlist =
  pwdchecks =

root:
  admin = true
  SYSTEM = "compat"
  registry = files
  loginretries = 0
  account_locked = false
  rlogin = false

daemon:
  admin = true
  expires = 0101000070

bin:
  admin = true
  expires = 0101000070

sys:
  admin = true
  expires = 0101000070

adm:
  admin = true

uucp:
  admin = true
  login = false
  rlogin = false
  su = true

guest:

nobody:
  admin = true
  expires = 0101000070

lpd:
  admin = true
  expires = 0101000070

invscout:
  admin = true

snapp:
  admin = false
  rlogin = false
  su = false
  SYSTEM = "NONE"
  login = true
  ttys = /dev/tty0
  registry = files
  dce_export = false

ipsec:
  admin = false

nuucp:
  admin = false

esaadmin:
  admin = true

dasusr1:
  admin = false

db2inst1:
  admin = false
  umask = 22

db2fenc1:
  admin = false

麻烦大侠帮忙分析分析，问题处在了哪里，如何解决？
谢谢