This is the Name Service Cache Daemon. It takes care of group and password lookups for running programs and then caches the lookup results for the next query for services that can experience slowness in picking up changes such as NIS or LDAP. If you’re running these services, you may want to run nscd.
This daemon can cache data for name services, /etc/hosts, DNS, NIS, NIS+ etc. This is only for local users on the machine, because the cache is realized by wrapping the functions in glibc, remote user can never use this cache. It takes a time to change the cache even when the original DNS data is changed, therefore be careful to use this daemon.
Service Control
Example of “chkconfig –list [service]”
# chkconfig --list nscd nscd 0:off 1:off 2:off 3:off 4:off 5:off 6:off
Available service usage options:
# service nscd
Usage: /etc/init.d/nscd {start|stop|status|restart|reload|condrestart} Starting the service:
# service nscd start Starting nscd: [ OK ]
Stopping the service:
# service nscd stop Stopping nscd: [ OK ]
Check the status of the service:
# service nscd status nscd (pid 15382) is running...
Restarting the service:
# service nscd restart Stopping nscd: [ OK ] Starting nscd: [ OK ]
Reloading the service to re-read the configuration file:
# service nscd reload Reloading nscd: [ OK ]
Conditional restart of the service:
# service nscd condrestart Stopping nscd: [ OK ] Starting nscd: [ OK ]
– Which daemons does it run : /usr/sbin/nscd
– Which modules does it load : none
Configuration
Example configuration file:
# nscd will run as "nscd" user and not as root.
server-user nscd
# nscd set no debug output. if level is higher than 0, nscd will create some debug output, the higher the level, the more output is produced
debug-level 0
# disable paranoia mode, nscd will not restart itself periodically
paranoia no
# enables the specified service "passwd" cache
enable-cache passwd yes
# Sets the TTL (time-to-live) for positive entries (successful queries) in the specified cache for "passwd" to 600 seconds
positive-time-to-live passwd 600
# Sets the TTL (time-to-live) for negative entries (unsuccessful queries) in the specified cache for "passwd" to 20 seconds
negative-time-to-live passwd 20
# Sets the internal hash table size to 211
suggested-size passwd 211
# Enables checking the file belonging to the specified service "passwd" for changes
check-files passwd yes
# Keep the content of the cache for service "passwd" over server restarts;
persistent passwd yes
# The memory mapping of the nscd databases for service "passwd" is shared with the clients
shared passwd yes
# The maximum allowable size for the service "passwd" set to be 33554432 bytes
max-db-size passwd 33554432
# The .byname requests will add to passwd.byuid or group.bygid cache.
auto-propagate passwd yes Troubleshooting
Sometimes restart, stop or start of the NSCD daemon, it will not flush it’s cache, you need use following method to explicitly flush the old cache:
Before CentOS/RHEL 7:
# service nscd reload
After CentOS/RHEL 7:
# systemctl restart nscd