40.6 Process Information

Several functions return information about processes.

Command: list-processes &optional query-only buffer

This command displays a listing of all living processes. In addition, it finally deletes any process whose status was ‘Exited’ or ‘Signaled’. It returns nil.

The processes are shown in a buffer named *Process List* (unless you specify otherwise using the optional argument buffer), whose major mode is Process Menu mode.

If query-only is non-nil, it only lists processes whose query flag is non-nil. See Querying Before Exit.

Function: process-list

This function returns a list of all processes that have not been deleted.

     ⇒ (#<process display-time> #<process shell>)
Function: num-processors &optional query

This function returns the number of processors, a positive integer. Each usable thread execution unit counts as a processor. By default, the count includes the number of available processors, which you can override by setting the OMP_NUM_THREADS environment variable of OpenMP. If the optional argument query is current, this function ignores OMP_NUM_THREADS; if query is all, this function also counts processors that are on the system but are not available to the current process.

Function: get-process name

This function returns the process named name (a string), or nil if there is none. The argument name can also be a process object, in which case it is returned.

(get-process "shell")
     ⇒ #<process shell>
Function: process-command process

This function returns the command that was executed to start process. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program. For a network, serial, or pipe connection, this is either nil, which means the process is running or t (process is stopped).

(process-command (get-process "shell"))
     ⇒ ("bash" "-i")
Function: process-contact process &optional key no-block

This function returns information about how a network, a serial, or a pipe connection was set up. When key is nil, it returns (hostname service) for a network connection, (port speed) for a serial connection, and t for a pipe connection. For an ordinary child process, this function always returns t when called with a nil key.

If key is t, the value is the complete status information for the connection, server, serial port, or pipe; that is, the list of keywords and values specified in make-network-process, make-serial-process, or make-pipe-process, except that some of the values represent the current status instead of what you specified.

For a network process, the values include (see make-network-process for a complete list):


The associated value is the process buffer.


The associated value is the process filter function. See Process Filter Functions.


The associated value is the process sentinel function. See Sentinels: Detecting Process Status Changes.


In a connection, the address in internal format of the remote peer.


The local address, in internal format.


In a server, if you specified t for service, this value is the actual port number.

:local and :remote are included even if they were not specified explicitly in make-network-process.

For a serial connection, see make-serial-process and serial-process-configure for the list of keys. For a pipe connection, see make-pipe-process for the list of keys.

If key is a keyword, the function returns the value corresponding to that keyword.

If process is a non-blocking network stream that hasn’t been fully set up yet, then this function will block until that has happened. If given the optional no-block parameter, this function will return nil instead of blocking.

Function: process-id process

This function returns the PID of process. This is an integral number that distinguishes the process process from all other processes running on the same computer at the current time. The PID of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists. For network, serial, and pipe connections, this function returns nil.

Function: process-name process

This function returns the name of process, as a string.

Function: process-status process-name

This function returns the status of process-name as a symbol. The argument process-name must be a process, a buffer, or a process name (a string).

The possible values for an actual subprocess are:


for a process that is running.


for a process that is stopped but continuable.


for a process that has exited.


for a process that has received a fatal signal.


for a network, serial, or pipe connection that is open.


for a network, serial, or pipe connection that is closed. Once a connection is closed, you cannot reopen it, though you might be able to open a new connection to the same place.


for a non-blocking connection that is waiting to complete.


for a non-blocking connection that has failed to complete.


for a network server that is listening.


if process-name is not the name of an existing process.

(process-status (get-buffer "*shell*"))
     ⇒ run

For a network, serial, or pipe connection, process-status returns one of the symbols open, stop, or closed. The latter means that the other side closed the connection, or Emacs did delete-process. The value stop means that stop-process was called on the connection.

Function: process-live-p process

This function returns non-nil if process is alive. A process is considered alive if its status is run, open, listen, connect or stop.

Function: process-type process

This function returns the symbol network for a network connection or server, serial for a serial port connection, pipe for a pipe connection, or real for a subprocess created for running a program.

Function: process-exit-status process

This function returns the exit status of process or the signal number that killed it. (Use the result of process-status to determine which of those it is.) If process has not yet terminated, the value is 0. For network, serial, and pipe connections that are already closed, the value is either 0 or 256, depending on whether the connection was closed normally or abnormally.

Function: process-tty-name process &optional stream

This function returns the terminal name that process is using for its communication with Emacs—or nil if it is using pipes instead of a pty (see process-connection-type in Creating an Asynchronous Process). By default, this function returns the terminal name if any of process’s standard streams use a terminal. If stream is one of stdin, stdout, or stderr, this function returns the terminal name (or nil, as above) that process uses for that stream specifically. You can use this to determine whether a particular stream uses a pipe or a pty.

If process represents a program running on a remote host, this function returns the local terminal name that communicates with process; you can get the terminal name used by that program on the remote host with the process property remote-tty. If process represents a network, serial, or pipe connection, this function always returns nil.

Function: process-coding-system process

This function returns a cons cell (decode . encode), describing the coding systems in use for decoding output from, and encoding input to, process (see Coding Systems).

Function: set-process-coding-system process &optional decoding-system encoding-system

This function specifies the coding systems to use for subsequent output from and input to process. It will use decoding-system to decode subprocess output, and encoding-system to encode subprocess input.

Every process also has a property list that you can use to store miscellaneous values associated with the process.

Function: process-get process propname

This function returns the value of the propname property of process.

Function: process-put process propname value

This function sets the value of the propname property of process to value.

Function: process-plist process

This function returns the process plist of process.

Function: set-process-plist process plist

This function sets the process plist of process to plist.