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munged - Man Page

MUNGE daemon


munged [OPTION]...


The munged daemon is responsible for authenticating local MUNGE clients and servicing their credential encode & decode requests.

All munged daemons within a security realm share a common key. All hosts within this realm are expected to have common users/UIDs and groups/GIDs.  The key is used to cryptographically protect the credentials; it is created with the mungekey command.

When a credential is created, munged embeds metadata within it including the effective UID and GID of the requesting client (as determined by munged) and the current time (as determined by the local clock). It then compresses the data, computes a message authentication code, encrypts the data, and base64-encodes the result before returning the credential to the client.

When a credential is validated, munged first checks the message authentication code to ensure the credential has not been subsequently altered.  Next, it checks the embedded UID/GID restrictions to determine whether the requesting client is allowed to decode it.  Then, it checks the embedded encode time against the current time; if this difference exceeds the embedded time-to-live, the credential has expired.  Finally, it checks whether this credential has been previously decoded on this host; if so, the credential has been replayed.  If all checks pass, the credential metadata and payload are returned to the client.


-h,  --help

Display a summary of the command-line options.

-L,  --license

Display license information.

-V,  --version

Display version information.

-f,  --force

Force the daemon to run if at all possible.  This overrides warnings for an existing local domain socket, a lack of entropy for the PRNG, and insecure file/directory permissions.  Use with caution as overriding these warnings can affect security.

-F,  --foreground

Run the daemon in the foreground.

-M,  --mlockall

Lock all current and future pages in the virtual memory address space. Access to locked pages will never be delayed by a page fault.  This can improve performance and help the daemon remain responsive when the system is under heavy memory pressure.  This typically requires root privileges or the CAP_IPC_LOCK capability.

-s,  --stop

Stop the daemon bound to the socket and wait for it to shut down.  Use with the --socket option to target a daemon bound to a non-default socket location.  This option exits with a zero status if the specified daemon was successfully stopped, or a non-zero status otherwise.

-S,  --socket path

Specify the local domain socket for communicating with clients.

-v,  --verbose

Be verbose.

--auth-server-dir directory

Specify an alternate directory in which the daemon will create the pipe used to authenticate clients.  The recommended permissions for this directory are 0711.  This option is only valid on platforms where client authentication is performed via a file-descriptor passing mechanism.

--auth-client-dir directory

Specify an alternate directory in which clients will create the file used to authenticate themselves to the daemon.  The recommended permissions for this directory are 1733.  This option is only valid on platforms where client authentication is performed via a file-descriptor passing mechanism.


Disable recurring timers in order to reduce some noise while benchmarking. This affects the PRNG entropy pool, supplementary group mapping, and credential replay hash.  Do not enable this option when running in production.

--group-check-mtime boolean

Specify whether the modification time of /etc/group should be checked before updating the supplementary group membership mapping.  If this value is non-zero, the check will be enabled and the mapping will not be updated unless the file has been modified since the last update.

--group-update-time seconds

Specify the number of seconds between updates to the supplementary group membership mapping; this mapping is used when restricting credentials by GID. A value of 0 causes it to be computed initially but never updated (unless triggered by a SIGHUP).  A value of -1 causes it to be disabled.

--key-file path

Specify an alternate pathname to the key file.

--listen-backlog integer

Specify the socket's listen backlog limit; note that the kernel may impose a lower limit.  A value of 0 uses the software default.  A value of -1 specifies SOMAXCONN, the maximum listen backlog queue length defined in <sys/socket.h>.

--log-file path

Specify an alternate pathname to the log file.

--max-ttl integer

Specify the maximum allowable time-to-live value (in seconds) for a credential. This setting has an upper-bound imposed by the hard-coded MUNGE_MAXIMUM_TTL value.  Reducing it will limit the maximum growth of the credential replay cache.  This is viable if clocks within the MUNGE realm can be kept in sync with minimal skew.

--num-threads integer

Specify the number of threads to spawn for processing credential requests.

--origin address

Specify the origin address that will be encoded into credential metadata. This can be a hostname or IPv4 address; it can also be the name of a local network interface, in which case the first IPv4 address found assigned to that interface will be used.  The default value is the IPv4 address of the hostname returned by gethostname().  Failure to lookup the address will result in an error; if overridden, the origin will be set to the null address.

--pid-file path

Specify an alternate pathname for storing the Process ID of the daemon.

--seed-file path

Specify an alternate pathname to the PRNG seed file.


Redirect log messages to syslog when the daemon is running in the background.

--trusted-group group

Specify the group name or GID of the "trusted group".  This is used for permission checks on a directory hierarchy.  Directories with group write permissions are allowed if they are owned by the trusted group (or the sticky bit is set).



Immediately update the supplementary group membership mapping instead of waiting for the next scheduled update; this mapping is used when restricting credentials by GID.


Terminate the daemon.


All clocks within a security realm must be kept in sync within the credential time-to-live setting.

While munged prevents a given credential from being decoded on a particular host more than once, nothing prevents a credential from being decoded on multiple hosts within the security realm before it expires.


Chris Dunlap <cdunlap@llnl.gov>

See Also

munge(1), remunge(1), unmunge(1), munge(3), munge_ctx(3), munge_enum(3), munge(7), mungekey(8).


Referenced By

munge(1), munge(3), munge(7), munge_ctx(3), munge_enum(3), mungekey(8), remunge(1), unmunge(1).

2024-03-15 munge-0.5.16 MUNGE Uid 'N' Gid Emporium