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Operating Systems Linux Red Hat Could not resolve ip through DNS Post 302986543 by Scrutinizer on Sunday 27th of November 2016 04:16:37 AM
Old 11-27-2016
Perhaps the host cache needs to be invalidated (nscd, sssd)? What OS and version are you using?

From man nscd of an old version of nscd for example:
Code:
NOTES

       Nscd doesn't know anything about the underlaying protocols for  a  ser-
       vice.  This  also  means,  that  if you change /etc/resolv.conf for DNS
       queries, nscd will continue to use the old one if you  have  configured
       /etc/nsswitch.conf  to  use  DNS  for host lookups. In such a case, you
       need to restart nscd.

Newer version of nscd try to watch for changes to this file, but even then there may be a delay..

See for example here:
https://www.unix.com/man-page/linux/8/nscd/

Code:
NOTES
       The daemon will try to watch for changes in configuration files appropriate for each data-
       base (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 cache:

	   $ nscd -i <database>

 

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nscd(1M)						  System Administration Commands						  nscd(1M)

NAME
nscd - name service cache daemon SYNOPSIS
/usr/sbin/nscd [-f configuration-file] [-g] [-e cachename, yes | no] [-i cachename] DESCRIPTION
nscd is a process 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(4). nscd provides caching for the passwd(4), group(4), hosts(4), ipnodes(4), exec_attr(4), prof_attr(4), and user_attr(4) databases through standard libc interfaces, such as gethostbyname(3NSL), getipnodebyname(3SOCKET), gethostbyaddr(3NSL), and others. Each cache has a separate time-to-live for its data; modifying the local database (/etc/hosts, /etc/resolv.conf, and so forth) causes that cache to become invali- dated upon the next call to nscd. The shadow file is specifically not cached. getspnam(3C) calls remain uncached as a result. nscd also acts as its own administration tool. If an instance of nscd is already running, commands are passed to the running version trans- parently. In order to preserve NIS+ security, the nscd service checks the permissions on the passwd table if NIS+ is being used. If this table cannot be read by unauthenticated users, then nscd will make sure that any encrypted password information returned from the NIS+ server is sup- plied only to the owner of that password. OPTIONS
Several of the options described below require a cachename specification. Supported values are passwd, group, hosts, ipnodes, exec_attr, prof_attr, and user_attr. -f configuration-file Causes nscd to read its configuration data from the specified file. -g Prints current configuration and statistics to standard output. This is the only option executable by non-root users. -e cachename, yes|no Enables or disables the specified cache. -i cachename Invalidate the specified cache. EXAMPLES
Example 1: Stopping and restarting the nscd daemon. example# svcadm disable system/name-service-cache example# svcadm enable system/name-service-cache FILES
/etc/nscd.conf Determines athe behavior of the cache daemon ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
svcs(1), svcadm(1M), getspnam(3C), gethostbyname(3NSL), getipnodebyname(3SOCKET), exec_attr(4), group(4), hosts(4), ipnodes(4), nscd.conf(4), nsswitch.conf(4), passwd(4), prof_attr(4), user_attr(4), attributes(5), NOTES
The output from the -g option to nscd is subject to change. Do not rely upon it as a programming interface. The nscd service is managed by the service management facility, smf(5), under the service identifier: svc:/system/name-service-cache Administrative actions on this service, such as enabling, disabling, or requesting restart, can be performed using svcadm(1M). The ser- vice's status can be queried using the svcs(1) command. SunOS 5.10 30 Oct 2003 nscd(1M)
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