Even if I have a lot of free space PgSQL returns "ERROR: could not extend file - No space left on device"

Dear Pg-users,

I am coming back to Postgres/PostGIS after a few years. I am dealing with a
big database with a lot of geometries and too many vertices.

After hours running a query to Subdivide, I get this Postgres error

*2023-09-08 02:11:23.745 BST [328594] postgres(at)database ERROR: could not
extend file "base/16388/7985375.1020": No space left on device 2023-09-08
02:11:23.745 BST [328594] postgres(at)database HINT: Check free disk space.*

2023-09-08 02:11:23.745 BST [328594] postgres(at)database STATEMENT: CREATE
TABLE _gaul_administrative_subdivided100 AS (
SELECT *, st_subdivide(geom,100) AS geom_subdivided100
FROM gaul_administrative
);

*2023-09-08 02:15:38.251 BST [313729] LOG: checkpoint complete: wrote
81956 buffers (1.6%); 0 WAL file(s) added, 0 removed, 608 recycled;
write=269.414 s, sync=0.001 s, total=269.634 s; sync files=1, longest=0.001
s, average=0.001 s; distance=9962549 kB, estimate=9980351 kB;
lsn=291/BF46ABE8, redo lsn=291/A0FB7D98*

It seems that it is not a problem of space.

Command *df -h* returns:

Filesystem Size Used Avail Use% Mounted on
tmpfs 6.3G 1.1M 6.3G 1% /run
/dev/sda 1.3T 164G 1.1T 14% /
tmpfs 32G 3.2M 32G 1% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 6.3G 4.0K 6.3G 1% /run/user/1000

Command *df -ih* returns:

Filesystem Inodes IUsed IFree IUse% Mounted on
tmpfs 7.9M 724 7.9M 1% /run
/dev/sda 80M 179K 80M 1% /
tmpfs 7.9M 4 7.9M 1% /dev/shm
tmpfs 7.9M 3 7.9M 1% /run/lock
tmpfs 1.6M 28 1.6M 1% /run/user/1000

I suppose it is an issue with temporary table, here my present
configuration in *postgresql.conf*

#temp_tablespaces = '' # a list of tablespace names,
'' uses
# only default tablespace

#temp_file_limit = -1 # limits per-process temp file
space
# in kilobytes, or -1 for no limit

What do you suggest?

cheers,

Enzopolo