system mounts /dev/loop0 on /snap/core/3604 and it's 100% full, where is it coming from? [duplicate]

Solution 1:

and it's always 100% full

That is normal. /dev/loopX are virtual devices to mount image files. And they are -read only- so do not get larger or smaller than they are when created.

Those mount points are connected to the snapd service. You will see extra loop devices added for every software you install using "snap". Libreoffice has a snap, VLC has one.

From my system:

rinzwind@schijfwereld:~$ df -H
Filesystem      Size  Used Avail Use% Mounted on
...
/dev/loop0       88M   88M     0 100% /snap/core/3440
/dev/loop2       88M   88M     0 100% /snap/core/3604
/dev/loop1      204M  204M     0 100% /snap/vlc/65
/dev/loop3       88M   88M     0 100% /snap/core/3247
/dev/loop4      121M  121M     0 100% /snap/vlc/4

I have installed VLC from a snap install so I have 2 extra named "vlc". "core" is used for snapd itself. Remove the service and those loop devices disappear with it (sudo apt purge snapd ubuntu-core-launcher squashfs-tools would remove it; but I would leave it as is if I was you).

++++++++++++++++++++++++++ additional info:

maximum@maxipc:~$ systemctl status snap-core-3604.mount

● snap-core-3604.mount - Mount unit for core
   Loaded: loaded (/etc/systemd/system/snap-core-3604.mount; enabled; vendor pre
   Active: active (mounted) since Wed 2017-12-27 15:44:36 EST; 2min 6s ago
    Where: /snap/core/3604
     What: /dev/loop0
  Process: 838 ExecMount=/bin/mount /var/lib/snapd/snaps/core_3604.snap /snap/co

Dec 27 15:44:36 maxipc systemd[1]: Mounting Mount unit for core...
Dec 27 15:44:36 maxipc systemd[1]: Mounted Mount unit for core.