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Man 8 munged

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Chris Dunlap edited this page Feb 4, 2016 · 18 revisions

Name

munged -- MUNGE daemon

Synopsis

munged [OPTION] ...

Description

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 secret key. This key is used to protect the contents of a credential.

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.

Options

  • -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, --socket path
    Specify the local domain socket for communicating with clients.

  • --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.

  • --benchmark
    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 integer
    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 file
    Specify an alternate secret key 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. [Added in 0.5.12]

  • --num-threads integer
    Specify the number of threads to spawn for processing credential requests.

  • --pid-file path
    Specify an alternate pathname for storing the Process ID of the daemon. [Added in 0.5.12]

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

Signals

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

  • SIGTERM
    Terminate the daemon.

Notes

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.

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