CEPH-MON(8)

💅 NAME 💅

ceph-mon — the ceph monitor daemon ✨ (yes that's the whole name section, she's lowkey mysterious, we love that for her)

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🦋 SYNOPSIS 🦋

ceph-mon -i monid [ --mon-data mondatapath ]

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👑 DESCRIPTION 👑

okay so picture this: ceph-mon is the cluster monitor daemon for the Ceph distributed file system. she's the one holding the group chat together 🫶

one or more instances of ceph-mon team up to form a Paxos part-time parliament cluster (yes, that's the real name, and yes, it's giving congress-but-make-it-durable). together they provide extremely reliable and durable storage of cluster membership, configuration, and state. no cap. that's the whole job and they slay at it.

the mondatapath is a directory on a local file system that stores monitor data. it's normally specified via the mon data option in the configuration file. (translation: she has a lil home folder and you gotta tell her where it is 💖)

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✨ OPTIONS ✨

• -f, --foreground — Foreground mode, bestie: do not daemonize after startup (so she just runs in the foreground like a normal main character). also, do not generate a pid file. super useful when you're running her via ceph-run(8).
• -d — Debug mode: it's like -f but extra, because it also sends all log output to stderr. 💀
• --setuser userorgid — set the uid after starting. if you hand her a username, the user record gets looked up to grab a uid and a gid, and that gid gets set too — unless --setgroup is also specified, in which case she minds her business.
• --setgroup grouporgid — set the gid after starting. if you give her a group name, the group record is looked up to get a gid.
• -c ceph.conf, --conf=ceph.conf — use this ceph.conf configuration file instead of the default /etc/ceph/ceph.conf to determine monitor addresses during startup. (default file found crying in the /etc/ceph corner 😭)
• --mkfs — initialize the mon data directory with seed information so she can form an initial ceph file system or join an existing monitor cluster. three (3) pieces of info must be provided, no exceptions:
  • the cluster fsid. this can come from a monmap (--monmap <path>) or explicitly via --fsid <uuid>.
  • a list of monitors and their addresses. this list of monitors can come from a monmap (--monmap <path>), the mon host configuration value (in ceph.conf or via -m host1,host2,...), or — for backward compatibility only, it's deprecated bestie — the mon addr lines in ceph.conf. if this monitor is meant to be part of the initial monitor quorum for a new Ceph cluster, then it must be included in the initial list, matching either the name or the address of a monitor in the list. when you're matching by address, either the public addr or public subnet options may be used.
  • the monitor secret key mon. — this one must be included in the keyring provided via --keyring <path>.
• --keyring — specify a keyring for use with --mkfs. 🎀
• --use-mon-keyring — use the mon's keyring file as authoritative for the mon. secret. normally the key in the mons' auth database is the one getting the job.
• --no-config-file — signal that we do not want to rely on a ceph.conf, whether user provided or the default one, to run the daemon. heads up: this means you'll have to hand every necessary option to the daemon as arguments. all of them. yourself. 💅

real talk: --mkfs will absolutely not guess for you. no fsid, no monitor list, no mon. key in the keyring → no monitor. she's not doing improv.

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🌈 AVAILABILITY 🌈

ceph-mon is part of Ceph — a massively scalable, open-source, distributed storage system. for more info, please refer to the Ceph documentation at https://docs.ceph.com 📚✨

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🫶 SEE ALSO 🫶

ceph(8), ceph-mds(8), ceph-osd(8) — the rest of the squad, go say hi 🦋

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🍓 Copyright 🍓

2010-2014, Inktank Storage, Inc. and contributors. Licensed under Creative Commons Attribution Share Alike 3.0 (CC-BY-SA-3.0) 💜

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aaaand that's a wrap bestie 🎀 this was written by dev, dated Oct 06, 2026, and lives under the manual page name CEPH-MON(8). go forth and monitor responsibly, mwah 💖✨👑