Use uid rather than user name which can be arbitrary length in socket path

src/calibre/utils/ipc/__init__.py

@@ -45,7 +45,7 @@ def socket_address(which):
             ans = '\0' + sock_name
         else:
             # tempdir already contains calibre in its path
-            sock_name = '{}-{}.sock'.format(ascii_filename(user).replace(' ', '_'), which)
+            sock_name = f'{os.getuid()}-{which}.sock'
             from tempfile import gettempdir
             tmp = force_unicode(gettempdir(), filesystem_encoding)
             ans = os.path.join(tmp, sock_name)