MQRC 2537: Channel unavailable

What it means

A client connection runs over an instance of a server-connection (SVRCONN) channel on the queue manager. Unlike 2538, where the client can't reach the host at all, 2537 means the network path worked and the queue manager answered, but it refused to start a channel instance for this client.

IBM lists five reasons. The channel is in STOPPED state. A channel exit stopped it. The client has reached the limit of instances of this channel allowed from one client, set by MAXINSTC. The channel has reached its total instance limit, set by MAXINST. Or the queue manager has reached its limit on channels overall, set by MaxChannels in the CHANNELS stanza of qm.ini on distributed MQ, or by the MAXCHL queue manager attribute on z/OS.

The instance limits are often hit by a leak, not by real load. An application server that opens connections without closing them, or a pool sized larger than the limits allow, uses up instances until new connects fail. The same reason code identifies the Channel Not Available event, which channel events can report.

Common causes

• The server-connection channel was stopped with STOP CHANNEL, and left in STOPPED state.
• The application reached MAXINSTC, the instances allowed from one client, often because of a connection leak or too large a connection pool.
• All clients together reached MAXINST on that channel.
• The queue manager reached its overall channel limit (MaxChannels on distributed MQ, MAXCHL on z/OS).
• A channel security or other exit decided to stop the channel.

How to find the problem

1. Read the queue manager error log at the time of the failure. It says which limit was hit or that the channel is stopped. Also check the client error log.
2. Check the channel definition with DISPLAY CHANNEL(APP.SVRCONN) MAXINST MAXINSTC SHARECNV.
3. Count running instances with DISPLAY CHSTATUS(APP.SVRCONN) CONNAME STATUS. Many instances from the same CONNAME point to a leak or an oversized pool.
4. A STATUS of STOPPED in DISPLAY CHSTATUS means the channel was stopped and will refuse clients until someone starts it.
5. On distributed MQ, read MaxChannels in qm.ini. On z/OS, use DISPLAY QMGR MAXCHL and DISPLAY CHINIT to see current and maximum channel counts.

How to fix it

• If the channel was stopped, find out why, then run START CHANNEL(APP.SVRCONN). For a server-connection channel this lets clients connect again.
• Fix connection leaks so the application disconnects or returns connections to its pool.
• Size connection pools to fit within MAXINSTC, or raise MAXINSTC and MAXINST with ALTER CHANNEL(...) CHLTYPE(SVRCONN) if the load is real.
• Raise the queue manager's channel limit if many applications share it, and restart where the platform requires it.
• Keep a margin. Set the limits high enough for normal peaks but low enough that one runaway client can't take every channel.

What it looks like

JMSWMQ0018: Failed to connect to queue manager 'QM1' with connection mode 'Client' and host name 'mqhost01(1414)'.
JMSCMQ0001: IBM MQ call failed with compcode '2' ('MQCC_FAILED') reason '2537' ('MQRC_CHANNEL_NOT_AVAILABLE').

Technical reviewer: Albert Joseph, WND Software.

Last reviewed 2026-10-18 by the WND Software team. Written in our own words. For the full reference, check IBM’s MQ documentation for your version.