Posts etiquetados ‘dns’

To integrate a Linux system with a centralized user directory (like Microsoft Active Directory) the usual solution is to configure Kerberos for Authentication (password/credential checking) and LDAP for Authorization and Access Control. The “standarized” way to implement this is using libpam_krb5libnss_ldap (by padl software) and nscd (from libc).

Kerberos integration works pretty well and I do not have too many issues with it, but I can not say the same from libnss_ldap and nscd.

In this post I will explain the anoying problems that you can find using libnss_ldap and nscd, and propose some solutions and configurations that will make it work properly. I also recomend read a previous post about the problems and solutions with connecting an Unix server to Active directory (Spanish post).

Read this article if you are experiencing problems with nscd+libnss_ldap (quoting http://www.nico.schottelius.org/blog/nscd-bugs/):

  • Sometimes it consumes 100% cpu (and does not stop that until being killed)
  • Sometimes it just crashes.
  • Sometimes it causes users to “vanish”
  • Sometimes it hangs and thus slows down the whole system
  • Sometimes it makes all the host work slow
  • Sometimes login a host or execute sudo/su takes a lot of time or never logins.
  • Sometimes sudo or su dies with “Segmentation Fault”
  • Sometimes a simple ‘ls’ command takes minutes.
  • etc…

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AIX has the following (inefficient) mechanism to resolve network names (DNS): It will ask each nameserver in /etc/resolv.conf always secuencially, one per one, waiting an amount of time (RES_TIMEOUT) until each of the servers respond or timeouts. If all of them are down, it will retry again defined number of times (RES_RETRY), doubling the timeout each cicle. This is really annoying specially in the worse moment: when you have problems.

In this post I will test and comment this behaviour and propose some solutions.

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