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nscd - name service cache daemon
Nscd is a daemon that provides a cache for the most common name
service requests. The default configuration file, /etc/nscd.conf,
determines the behavior of the cache daemon. See nscd.conf(5).
Nscd provides caching for accesses of the passwd(5), group(5), and
hosts(5) databases through standard libc interfaces, such as
getpwnam(3), getpwuid(3), getgrnam(3), getgrgid(3), gethostbyname(3),
There are two caches for each database: a positive one for items
found, and a negative one for items not found. Each cache has a
separate TTL (time-to-live) period for its data. Note that the
shadow file is specifically not cached. getspnam(3) calls remain
uncached as a result.
--help will give you a list with all options and what they do.
The daemon will try to watch for changes in configuration files
appropriate for each database (e.g., /etc/passwd for the passwd
database or /etc/hosts and /etc/resolv.conf for the hosts database),
and flush the cache when these are changed. However, this will
happen only after a short delay (unless the inotify(7) mechanism is
available and glibc 2.9 or later is available), and this auto-
detection does not cover configuration files required by nonstandard
NSS modules, if any are specified in /etc/nsswitch.conf. In that
case, you need to run the following command after changing the
configuration file of the database so that nscd invalidates its
$ nscd -i
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GNU 2012-05-10 NSCD(8)