四個字 堅持到底

# yppasswd user
New Password:
Re-enter new Password:
Permission denied
You might also find something like this in the debug log: Jul 23 08:45:06 nismaster yppasswdd[162]: [ID 467562 auth.error] yppasswdd: user someuser: does not exist

Solution
You match the following conditions:

you run your NIS out of a non-standard directory (ie not /var/yp) and have a custom /var/yp/Makefile which fixes NIS to this effect; and
you have recently run some Solaris patches, probably a Recommended or Recommended+Security patch set.
One of the patches helpfully "fixed" your non-standard /var/yp/Makefile back to the default. Un-fix this and restart yp, and you should be back in business. 

原因是更新完/var/yp/Makefile設定的passwd目錄位置被更改，重新指定就能解決。