I have a directory entry as follows
srwxr-xr-x 1 ubuntu ubuntu 0 May 29 05:03 0.0.0.0=
I do not know what the
s means and also that is a strange file name and I wonder what it is good for. Could this be garbage or is it something meaningful?
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The file type is one of the following characters:
‘-’ regular file
‘b’ block special file
‘c’ character special file
‘C’ high performance (“contiguous data”) file
‘D’ door (Solaris 2.5 and up)
‘l’ symbolic link
‘M’ off-line (“migrated”) file (Cray DMF)
‘n’ network special file (HP-UX)
‘p’ FIFO (named pipe)
‘P’ port (Solaris 10 and up)
‘?’ some other file type
So, that's a Unix socket. It could be meaningful, since sockets are created by processes to listen for requests. Use
lsof to determine what process is using that socket.
You may need to use
lsof, if the socket is opened by a process running as another user:
$ lsof /run/snapd.socket $ sudo lsof /run/snapd.socket lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs Output information may be incomplete. COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME systemd 1 root 197u unix 0xffff99dc9afa3000 0t0 191670 /run/snapd.socket type=STREAM snapd 18626 root 8u unix 0xffff99dc9afa3000 0t0 191670 /run/snapd.socket type=STREAM
To add up, this file type is also called special file there are multiple special files exist in UNIX (all of them are listed as part of ls manual, useful snippet is provided by muru).