After some (a lot of) research, I found an interesting topic:
https://help.nextcloud.com/t/failed-to-connect-to-nc/27814
This is a problem on MariaDB is stopped.
root@Nextcloud:/var/www/html/nextcloud/config# systemctl status mariadb.service
● mariadb.service - MariaDB 10.3.22 database server
Loaded: loaded (/lib/systemd/system/mariadb.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Sun 2021-01-17 17:28:28 CET; 18s ago
Docs: man:mysqld(8)
https://mariadb.com/kb/en/library/systemd/
Process: 6963 ExecStartPre=/usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld (code=exited, status=
Process: 6964 ExecStartPre=/bin/sh -c systemctl unset-environment _WSREP_START_POSITION (code=exited, status
Process: 6966 ExecStartPre=/bin/sh -c [ ! -e /usr/bin/galera_recovery ] && VAR= || VAR=`/usr/bin/galera_re
Process: 7014 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS $_WSREP_NEW_CLUSTER $_WSREP_START_POSITION (code=exite
Main PID: 7014 (code=exited, status=1/FAILURE)
Status: "MariaDB server is down"
janv. 17 17:28:23 Nextcloud systemd[1]: Starting MariaDB 10.3.22 database server...
janv. 17 17:28:23 Nextcloud mysqld[7014]: 2021-01-17 17:28:23 0 [Note] /usr/sbin/mysqld (mysqld 10.3.22-MariaD
janv. 17 17:28:28 Nextcloud systemd[1]: mariadb.service: Main process exited, code=exited, status=1/FAILURE
janv. 17 17:28:28 Nextcloud systemd[1]: mariadb.service: Failed with result 'exit-code'.
janv. 17 17:28:28 Nextcloud systemd[1]: Failed to start MariaDB 10.3.22 database server.
it was not launched due to a full disk
root@Nextcloud:/var/www/html/nextcloud/config# df
Sys. de fichiers blocs de 1K Utilisé Disponible Uti% Monté sur
udev 1006276 0 1006276 0% /dev
tmpfs 204216 5716 198500 3% /run
/dev/sda1 30832548 29244308 0 100% /
tmpfs 1021076 0 1021076 0% /dev/shm
tmpfs 5120 0 5120 0% /run/lock
tmpfs 1021076 0 1021076 0% /sys/fs/cgroup
tmpfs 204212 0 204212 0% /run/user/1000
I deleted some old backups, which made me recover some space.
root@Nextcloud:~# df
Sys. de fichiers blocs de 1K Utilisé Disponible Uti% Monté sur
udev 1006276 0 1006276 0% /dev
tmpfs 204216 5716 198500 3% /run
/dev/sda1 30832548 26182728 3060572 90% /
tmpfs 1021076 0 1021076 0% /dev/shm
tmpfs 5120 0 5120 0% /run/lock
tmpfs 1021076 0 1021076 0% /sys/fs/cgroup
tmpfs 204212 0 204212 0% /run/user/1000
I was able to restart apache correctly and recover my server. I still have to find out why I have 10% free space left.