Snaps update automatically, and by default, the snapd daemon checks for updates 4 times a day. Each update check is called a refresh.
Updates can be set to occur on Friday at midnight, or for specific days of the month, such as only the third Monday, or even the last Friday of the month, between 23:00 to 01:00 the next day. They can even be postponed indefinitely, or for a set period of time.
When, if, and how often, these updates occur can is the job of the snap refresh command.
Snaps running in devmode, or installed locally, are typically intended for testing and do not update automatically until they’ve been published and downloaded from the store.
Refresh update control
There are two general approaches to postponing or otherwise managing snap updates, with either the snap refresh --hold command, or with system settings:
Pause or stop updates with refresh hold
Control updates with system options
Pause or stop automatic updates
Requires: snapd 2.58+
The snap refresh --hold command holds, or postpones, snap updates for individual snaps, or for all snaps on the system, either indefinitely or for a specified period of time.
snap refresh --hold=<duration> <snap1> <snap2>...
Time duration units can be seconds (s), minutes (m) or hours (h), or a combination of these. To postpone updates indefinitely, a value of forever is also valid.
$ snap refresh --hold=24h firefox
General refreshes of "firefox" held until 2022-10-26T14:10:53+01:00
If no duration is specified, the time duration defaults to forever.
If no snaps are specified, the hold applies to all snaps installed on the system:
$ snap refresh --hold=24h
Auto-refresh of all snaps held until 2022-10-26T14:25:58+01:00
To see which snaps are being held, look for held in the notes column when running snap list:
$ snap list
Name Version Rev Tracking Publisher Notes
alacritty 0.8.0 46 latest/stable snapcrafters classic
vlc 3.0.18 3078 latest/stable videolan✓ -
yt-dlp 18 212 latest/edge morrisong held
However, there are important differences in how a hold is applied, depending on whether individual snaps are specified or not. These differences are described below.
If snaps are specified
The refresh hold is:
Effective on auto-refreshes and general snap refresh requests
Not effective on targeted snap refreshes
When one or more snaps are specified, the hold is effective only on their auto-refreshes and general refresh requests from snap refresh.
However, a refresh that targets a held snap specifically will not be blocked and will always be able to proceed.
This can be useful if a snap upgrade is known to be problematic. That specific snap can be held while the remainder of the system is safely refreshed. After the snap upgrade problem has been solved, and a new revision of the snap published, that snap can then be manually refreshed as a specific target. If the upgrade works as expected, the hold can be safely removed (see Remove a hold).
If no snaps are specified
The refresh hold is:
Effective only on auto-refreshes
Not effective on general snap refresh requests and targeted snap refreshes
If no snaps are specified, a hold applies to all snaps installed on the system, however the hold is only effective on auto-refreshes and will not block either general refresh requests from ‘snap refresh’, or specific snap requests from ‘snap refresh target-snap’.
Remove a hold
The snap refresh --unhold command removes a refresh hold, either for the specified snaps or for all snaps when no snaps are targeted specifically.
For a single snap:
$ snap refresh --unhold firefox
Removed general refresh hold of "firefox"
For for all snaps:
$ snap refresh --unhold
Removed auto-refresh hold on all snaps
Control updates with system options
The refresh rate is freely configurable, and can be set to any duration above a lower bound of once every 20 minutes. There are four system-wide options that manage how updates are handled:
refresh.timer: defines the refresh frequency and schedule
refresh.hold: delays the next refresh until the defined time and date
refresh.metered: pauses refresh updates when network connection is metered
refresh.retain: sets how many revisions of a snap are stored on the system
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:
Mondays at 10:00, Fridays at 15:00
Mondays at 10:00 and 15:00, Fridays at 10:00 and 15:00
Monday to Wednesday and on Friday, twice between 9:00 and 11:10
Mondays, some time between 9:00 and 11:00, and on Wednesdays, some time between 22:00 and 23:00
Monday and on Wednesday, at 0:00
2nd Monday of the month, through the following Wednesday, between 23:00 and 24:00
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
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 (up to 90 days). 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:
The correct format can be generated with the date command:
$ date --date="BST 2023-09-23 17:22:54" +%Y-%m-%dT%H:%M:%S%:z
$ sudo snap set system refresh.hold="$(date --date=tomorrow +%Y-%m-%dT%H:%M:%S%:z)"
$ sudo snap get system refresh.hold
After a refresh, the next refresh can be delayed by up to 90 days, after which a refresh will be performed regardless of the refresh.hold value.
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.metered 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 an Ubuntu LTS release.
Regardless of when a refresh is scheduled, an update refresh can be initiated with the snap refresh command:
$ snap refresh
gnome-system-monitor 3.28.2 from 'canonical' refreshed
gnome-calculator 3.28.2 from 'canonical' refreshed
The refresh command can also be used to see when the last refresh occurred and when the next is scheduled:
$ snap refresh --time
last: today at 09:16 GMT
next: today at 17:39 GMT
The first line in the above output shows the value of the timer system option. This defines how and when a refresh should be scheduled.
To see which snaps are going to be updated with the next refresh, use the additional --list argument:
Use the snap changes and snap tasks <change-id> commands to see details about what changed during the last refresh:
$ snap changes
ID Status Spawn Ready Summary
2052 Done today at 09:34 BST today at 09:35 BST Auto-refresh 7 snaps
2053 Done today at 15:16 BST today at 15:17 BST Refresh snaps "gnome-calculator", "flock-chat", "gnome-characters", "gnome-system-monitor"
Add the change-id to see what actions a specific change performed:
$ snap tasks 2053
Status Spawn Ready Summary
Done today at 15:16 BST today at 15:16 BST Ensure prerequisites for "gnome-calculator" are available
Done today at 15:16 BST today at 15:16 BST Download snap "gnome-calculator" (199) from channel "stable"
Done today at 15:16 BST today at 15:16 BST Fetch and check assertions for snap "gnome-calculator" (199)
Done today at 15:16 BST today at 15:16 BST Start snap "gnome-system-monitor" (54) services
Done today at 15:16 BST today at 15:16 BST Clean up "gnome-system-monitor" (54) install
Done today at 15:16 BST today at 15:16 BST Run configure hook of "gnome-system-monitor" snap if present