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Operating Systems Linux Red Hat Kernel thinks tcp port in use but isnt Post 302591440 by skkool22 on Thursday 19th of January 2012 12:58:39 PM
Old 01-19-2012
a colleague of mine used system tap to track the inet_csk_bind_conflict function and found that "nscd" process was the one hanging on to the tcp port.

this is what the system tap trace looked like:

inet_bind(nc): socket [state 1 type 1] uaddr 0.0.0.0:23426 addr_len 16
tcp_v4_get_port(nc): sock [reuse 1 state 7] snum 33371
bind_conflict(nc): sock [reuse 1 state 7] tb [port 33371 fastreuse 0 (reuse 0 state 7 owner (pid 0 uid 0 euid 0) uid 28 gid 28)]
bind_conflict: return 1 (EPERM)
tcp_v4_get_port: return 1 (EPERM)
inet_bind: return -98 (EADDRINUSE)

$ getent passwd 28
nscd:x:28:28:NSCD Daemon:/:/sbin/nologin

Restarting nscd freed up the port.

Anyway, 2 morals to the story:
1) I have some wicked smart colleagues.
2) when in doubt, restart nscd!
 

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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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