This is work in progress.
Snaps can provide a
check-health hook that can be used by developers to signal to the system and the user that something is not well with the snap. Note the health is of the snap, not of the apps it contains; it’s up to the snap developer to determine how the health of the individual apps add up to the health of the snap as a whole.
check-health hook is expected to use
snapctl to inform snapd about the health of the snap:
snapctl set-health [--code=<error code>] <status> [<message>]
status can be one of
okay(which takes no message [and no code?]),
waiting(some resource the snap needs isn’t ready yet, nothing for the user to do but wait message(+code) must explain what it’s waiting for)
blocked(the user needs to do something for the snap to do something; message(+code) must say what)
error(something went wrong; message+code must explain what broke)
There is another status that can’t be set by the snap directly:
unknown: the default, no hook provided or the hook did not call
code), or the hook itself failed (
codewill be set to
code is optional, meant to be used by the snap or related tooling. It is not a number, but a word with 3-30 bytes matching
snapctl set-health will fail if
code is invalid. The
snapd- prefix is reserved.
code is not allowed when
message is a freeform message (hopefully a full, properly capitalised sentence in English), that explains to the user what went wrong or what they need to do to unblock the snap. It should be at least 7 and no more than 70 bytes long, and will get truncated if the length is exceeded (but will fail if <7).
message is required if
status is not
okay, and not allowed if
The hook will be called periodically by snapd, so it’s important that it be fast, light, and idempotent; it will have a hard timeout of [TBD; 30 seconds?]. The user can trigger it manually with
snap health [<snap>...]. It will also be called as part of any install, refresh or revert operation.
When a snap’s health was
okay in one run, and in the next stopped being
okay, a warning will be emitted.
snap list will mention the last-known status of any snaps that have the health check hook, if the status is not
okay (or if the snap has a health check and the status is
snap info will include the full health information (but only in verbose mode if
okay or if
unknown with no health check hook).
~$ snap list some-broken-snap Name Version Rev Tracking Publisher Notes some-broken-snap 1234567 123 beta canonical✓ error ~$ snap info some-broken-snap # ... health: status: error message: Something went wrong. # not a very good message checked: 4 minutes ago code: oh-noes # Optional # ... ~$ snap health Snap status code Message a-nice-snap okay - - jump-drive waiting - Alcubierre drive spooling up. some-broken-snap error oh-noes Something went wrong