MUNGE(7) MUNGE Uid 'N' Gid Emporium MUNGE(7) NAME munge - MUNGE overview INTRODUCTION MUNGE (MUNGE Uid 'N' Gid Emporium) is an authentication service for creat- ing and validating user credentials. It is designed to be highly scalable for use in an HPC cluster environment. It provides a portable API for en- coding the user's identity into a tamper-proof credential that can be ob- tained by an untrusted client and forwarded by untrusted intermediaries within a security realm. Clients within this realm can create and validate credentials without the use of root privileges, reserved ports, or plat- form-specific methods. RATIONALE The need for MUNGE arose out of the HPC cluster environment. Consider the scenario in which a local daemon running on a login node receives a client request and forwards it on to remote daemons running on compute nodes within the cluster. Since the user has already logged on to the login node, the local daemon just needs a reliable means of ascertaining the UID and GID of the client process. Furthermore, the remote daemons need a mechanism to ensure the forwarded authentication data has not been subse- quently altered. A common solution to this problem is to use Unix domain sockets to deter- mine the identity of the local client, and then forward this information on to remote hosts via trusted rsh connections. But this presents several new problems. First, there is no portable API for determining the identity of a client over a Unix domain socket. Second, rsh connections must originate from a reserved port; the limited number of reserved ports available on a given host directly limits scalability. Third, root privileges are re- quired in order to bind to a reserved port. Finally, the remote daemons have no means of determining whether the client identity is authentic. MUNGE solves all of these problems. USAGE A process creates a credential by requesting one from the local MUNGE ser- vice, either via the munge_encode() C library call or the munge executable. The encoded credential contains the UID and GID of the originating process. This process sends the credential to another process within the security realm as a means of proving its identity. The receiving process validates the credential with the use of its local MUNGE service, either via the munge_decode() C library call or the unmunge executable. The decoded cre- dential provides the receiving process with a reliable means of ascertain- ing the UID and GID of the originating process. This information can be used for accounting or access control decisions. DETAILS The contents of the credential (including any optional payload data) are encrypted with a key shared by all munged daemons within the security realm. The integrity of the credential is ensured by a message authentica- tion code (MAC). The credential is valid for a limited time defined by its time-to-live (TTL); this presumes clocks within a security realm are in sync. Unexpired credentials are tracked by the local munged daemon in or- der to prevent replay attacks on a given host. Decoding of a credential can be restricted to a particular user and/or group ID. The payload data can be used for purposes such as embedding the destination's address to en- sure the credential is only valid on a specific host. The internal format of the credential is encoded in a platform-independent manner. And the credential itself is base64 encoded to allow it to be transmitted over vir- tually any transport. AUTHOR Chris Dunlap <cdunlap@llnl.gov> COPYRIGHT Copyright (C) 2007-2025 Lawrence Livermore National Security, LLC. Copyright (C) 2002-2007 The Regents of the University of California. MUNGE is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Additionally for the MUNGE library (libmunge), you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the Li- cense, or (at your option) any later version. SEE ALSO munge(1), remunge(1), unmunge(1), munge(3), munge_ctx(3), munge_enum(3), munged(8), mungekey(8). https://github.com/dun/munge munge-0.5.18 2026-02-10 MUNGE(7)
NAME | INTRODUCTION | RATIONALE | USAGE | DETAILS | AUTHOR | COPYRIGHT | SEE ALSO
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