SAP SM51 — SAP Servers
A production SAP system is rarely one machine. It is a system made of several application server instances, each running on a host, each with a set of work processes, all sharing one database.
Users are spread across those instances by the logon group they connect to. That means the work you are looking for is not necessarily happening on the instance you happen to be logged on to. This is the single most common reason a Basis investigation goes in circles: SM50 shows the work processes of your instance only, and the job you are hunting is on another one.
SM51 is the map. It lists the instances, shows which services each provides — dialog, update, enqueue, background, spool — and lets you double-click through into any of them.
The services matter. Only one instance runs the enqueue service, which manages the locks that stop two users editing the same document. Background work runs where batch work processes exist. Knowing which instance does what tells you where to look when something specific is wrong.
When you would actually use SM51
- Confirming that every application server instance is up and reachable.
- Finding which instance a job or a user session is running on before opening SM50.
- Checking which instance provides the enqueue service when locking behaves strangely.
- Getting the exact instance name to give to Basis or to SAP support.
What the screen looks like
| Server name | Host | Type | Status |
|---|---|---|---|
| sapprd01_PRD_00 | sapprd01 | Dialog Update Enqueue Batch Spool | Active |
| sapprd02_PRD_01 | sapprd02 | Dialog Batch Spool | Active |
| sapprd03_PRD_02 | sapprd03 | Dialog Batch | Active |
| sapprd04_PRD_03 | sapprd04 | Dialog Batch | Not reachable |
The fields, in plain English
The instance name, conventionally host_SID_instancenumber — so sapprd01_PRD_00 is instance 00 of system PRD on host sapprd01. This is the string SAP support and Basis will ask you for.
Watch out: The instance name is not the host name. One host can run more than one instance, and quoting the host alone is ambiguous.
The physical or virtual machine the instance runs on.
Which work process types the instance provides. Dialog serves interactive users, Update performs the database updates queued by dialog steps, Enqueue manages locks, Batch runs background jobs, Spool handles printing.
Watch out: Only one instance in the system runs the enqueue service. If lock behaviour is odd, that is the instance to look at, and it is usually the central one.
Whether the message server can currently reach the instance. An instance that stops being reachable is either down, or cut off from the message server by a network problem.
Step by step
- 1Open SM51 to list the instances.
- 2Check that every expected instance is present and active.
- 3Note which instance carries the enqueue service.
- 4Double-click an instance to open its work process overview.
- 5Use the system log for a specific instance when you need its errors rather than the whole system’s.
- 6When raising an incident, quote the full instance name, not just the host.
Errors you will hit, and what they mean
No connection to message server
Why: The message server is the component that keeps the instance list. If it is not reachable, SM51 has nothing to show.
Fix: This is a Basis matter and usually an outage rather than a user problem. Escalate rather than retry.
An expected instance is missing from the list
Why: The instance is stopped, or it started and failed to register with the message server.
Fix: Basis has to check the instance at the operating system level. From inside SAP you can only see that it is absent.
You are not authorised to display server information
Why: System administration objects restrict who can see instance and work process data.
Fix: A reasonable request for anyone doing support work, since SM51 changes nothing. Ask for display-level system monitoring rather than administration.
Common questions
What is the difference between SM51 and SM50?
SM50 shows the work processes of the instance you are logged on to, and only that one. SM51 shows all the instances in the system and lets you step into any of them. When someone says "I looked in SM50 and the job is not there", the answer is nearly always SM51 first.
What is the difference between SM51 and SM21?
SM51 is a list of servers and their status right now. SM21 is the system log — a historical record of errors and events, which can be read for one instance or for all of them. SM51 tells you which instance to look at; SM21 tells you what happened there.
Why is my work not on the server I logged on to?
Because logon groups distribute users across instances, and background jobs run wherever a batch work process is free. There is no guarantee your session and your job are on the same instance, which is precisely why SM51 exists.
Transactions that go with SM51
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