The Difference Between NSCD and UNSCD

Websites know who you are because NSCD works for you.

As people surf the Internet, their identities and personal information open doors. Usernames and passwords allow access to sites or forums, while cookies speed loading times for the sites that are frequently visited or assist in targeting advertisements to their audience. Behind the scenes, programs are needed to allow this to happen. NSCD and UNSCD are Linux specific daemons that do just that.

What Is NSCD?

NSCD stands for Name Service Cache Daemon. It handles all common name requests, notably passwords and group and host look-ups for running programs, as well as caching results to speed up the next query.

This package works in the GNU C library and relies on the standard libc interfaces. It should only be installed for slower services, including LDAP, NIS or NIS+, though it can boost DNS too.

Problems With NSCD

NSCD draws upon two databases, listing positive and negative results respectively. Problems have been caused when positive results are cached alongside negative ones. This can mask issues that are causing instability in the system. Also, the daemon ignores some DNS information, like TTLs, in programs like Solaris.

Users are encouraged to switch NSCD off when debugging their system. As a consequence, the cache is flushed, losing the recent information.

What Is UNSCD?

Despite the "U," UNSCD actually stands for Micro Name Service Cache Daemon. It is an NSCD that has been rewritten by Debian (debian.org) and performs all of the functions associated with that package.

UNSCD has been designed as a replacement drop-in for the original NSCD, so it has the same usage documentation. The two daemons should not be used together.

What Is the Difference Between NSCD and UNSCD?

In terms of functionality, there is no difference between NSCD and UNSCD, as one is an upgrade of the other.

Debian designed UNSCD to simplify the command code and to address some of the problems. Users have found this daemon to be the more stable and reliable of the two alternatives. It is recommended for those who do not wish to lose their cache when deactivating their NSCD. UNSCD is also a smaller program, as the code has been streamlined.

References

• Linus Documentation Project: Linux Dictionary
• Debian: Configuring LDAP Authentication
• Linux Documentation: Dictionary

Resources

• Arthur de Jong
• Russ Allbery: Flushing the NSCD Cache
• Evolvis Repository