check that the file exists:
ls -l ~/cardano-node/relay/db/node.socket
the result should begin with ‘s’
srwxr-xr-x 1 user group 0 Apr 30 07:59 node.socket
if exists then list the processes which using this socket file:
$ lsof storage/node.socket
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
cardano-n 6012 user 27u unix 0x0000000000000000 0t0 31984423 storage/node.socket type=STREAM