docs: def _remote_space_available_unix(self, search_pattern=""):
          """Return space available on *nix system (BSD/Linux)."""
          self.ssh_ctl_chan._enter_shell()
          remote_cmd = "/bin/df -k {}".format(self.file_system)
          remote_output = self.ssh_ctl_chan.send_command(
              remote_cmd, expect_string=r"[\$#]"
          )
  
          # Try to ensure parsing is correct:
          # Filesystem   1K-blocks  Used   Avail Capacity  Mounted on
          # /dev/bo0s3f    1264808 16376 1147248     1%    /cf/var
          remote_output = remote_output.strip()
          output_lines = remote_output.splitlines()
  
          # First line is the header; second is the actual file system info
          header_line = output_lines[0]
          filesystem_line = output_lines[1]
  
          if "Filesystem" not in header_line or "Avail" not in header_line.split()[3]:
              # Filesystem  1K-blocks  Used   Avail Capacity  Mounted on
              msg = "Parsing error, unexpected output from {}:\n{}".format(
                  remote_cmd, remote_output
              )
              raise ValueError(msg)
  
          space_available = filesystem_line.split()[3]
          if not re.search(r"^\d+$", space_available):
              msg = "Parsing error, unexpected output from {}:\n{}".format(
                  remote_cmd, remote_output
              )
              raise ValueError(msg)
  
          self.ssh_ctl_chan._return_cli()
          return int(space_available) * 1024