Snap supports a set of system-wide options that allow you to customise your snap environment.
As with Configuration in snaps, these options are changed with the set and get commands, but with a target of system instead of a specific snap:
$ snap set system some.option="some value"
$ snap get system some.option
There are three system-wide options that are used to manage various aspects of your snap environment handles update frequency:
Use refresh.timer to modify when, and how frequently, your snaps are refreshed.
The following example asks the system to only refresh snaps between 4.00am and 7.00am, and 7.00pm and 10:10pm:
$ sudo snap set system refresh.timer=4:00-7:00,19:00-22:10
Other examples for the time and frequency option include:
| Options | Result |
|---|---|
mon,10:00,,fri,15:00 |
Mondays at 10:00, Fridays at 15:10 |
mon,fri,10:00,15:00 |
Mondays at 10:00 and 15:00, Fridays at 10:00 and 15:00 |
mon-wed,fri,9:00-11:00/2 |
Monday to Wednesday and on Friday, twice between 9:00 and 11:10 |
mon,9:00~11:00,,wed,22:00~23:00 |
Mondays, some time between 9:00 and 11:00, and on Wednesdays, some time between 22:00 and 23:00 |
mon,wed |
Monday and on Wednesday, at 0:00 |
mon2-wed2,23:00-24:00 |
Monday through Wednesday on the 2nd week of the month, between 23:00 and 24:00 |
fri5,23:00-01:00 |
Last Friday of the month, from 23:00 to 1:00 the next day |
See Timer string format for a comprehensive breakdown of the syntax used to define times and frequencies.
You can check the update frequency for your environment with the refresh command:
$ snap refresh --time
timer: 00:00~24:00/4
last: today at 07:47 BST
next: today at 12:13 BST
By default, the snap system is scheduled to refresh four times per day, as shown in the above output.
Use refresh.hold to delay snap refreshes until a defined time and date. The time and date format needs to conform to RFC 3339.
For example, 5:22pm (BST), Tuesday 23rd April 2019, would look like the following:
2019-04-24T17:22:54+01:00
The correct format can be generated with the date command:
$ date --date="BST 2019-04-23 17:22:54" +%Y-%m-%dT%H:%M:%S%:z
2019-04-23T17:22:54+01:00
$ sudo sudo snap set system refresh.hold="$(date --date=tomorrow +%Y-%m-%dT%H:%M:%S%:z)"
$ sudo snap get system refresh.hold
2019-04-24T17:22:54+01:00
After a refresh, the next refresh can be delayed by up to 60 days, after which a refresh will be performed regardless of the refresh.hold value.
We explicitly format the date command output because the version of date provided by GNU core utilities breaks RFC3339 compatibility when passing the --rfc-3339 argument. See the bug report for further details.
Use refresh.metered to pause and re-enable the refresh process when NetworkManager detects a metered connection, such as an LTE link with a limited data plan.
To hold refreshing snaps when on a metered connection:
$ sudo snap set system refresh.metered=hold
To allow refreshing:
$ sudo snap set system refresh.metered=null
By default, refresh is enabled when a metered connection is detected.
Use refresh.retain to set the maximum number of a snap’s revisions stored by the system after the next refresh:
$ sudo snap set system refresh.retain=3
The refresh.retain value can be a number between 2 and 20. The default is refresh.retain=3 on Ubuntu Core systems and refresh.retain=2 on classic Ubuntu systems, such as those running Ubuntu 18.04 LTS (Bionic Beaver) and Ubuntu 16.04 LTS (Xenial Xerus).
These options may be set to change the proxies to be used by the system when communicating with external sites that speak the respective protocols.
Available since snapd 2.28.
May be set to true for disabling the SSH service at startup.
Available since snapd 2.22.
Defines the behaviour of the system when the power key is pressed.
May be set to one of:
Available since snapd 2.23.
Automatic snapshot retention time is configured with the snapshots.automatic.retention system option. The default value is 31 days, and the value needs to be greater than 24 hours:
$ snap set system snapshots.automatic.retention=30h
To disable automatic snapshots, set the retention time to no:
$ snap set system snapshots.automatic.retention=no
Disabling automatic snapshots will not affect pre-existing automatically generated snapshots, only those generated by subsequent snap removals.
Automatic snapshots require snap version 2.39+.
On a Raspberry Pi, the following options set corresponding values in the config.txt system configuration file:
Further details on the above, see the official Raspberry Pi documentation.
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