A session in dtach is a single instance in which a program is running under the control of dtach. The program is disassociated from the original terminal, and is thus protected from your original terminal being disconnected for some reason.

Other instances of dtach can attach themselves to a particular session. Input and output is copied between the program running in the dtach session, and the attached terminals.

dtach avoids interpreting the communication stream between the program and the attached terminals; it instead relies on the ability of the attached terminals to manage the screen.

Sessions are represented by Unix-domain sockets in the filesystem. No other permission checking other than the filesystem access checks is performed. dtach creates a master process that monitors the session socket, the program, and any attached terminals.

dtach has several modes of operation. It can create a new session in which a program is executed, or it can attach to an existing session. The first argument specifies which mode dtach should operate in.

-a

Attach to an existing session. dtach attaches itself to the session specified by <socket>. After the attach is completed, the window size of the current terminal is sent to the master process, and a redraw is also requested.

-A

Attach to an existing session, or create a new one. dtach first tries to attach to the session specified by <socket> if possible. If the attempt to open the socket fails, dtach tries to create a new session before attaching to it.

-c

Creates a new session. A new session is created in which the specified program is executed. dtach then tries to attach itself to the newly created session.

-n

Creates a new session, without attaching to it. A new session is created in which the specified program is executed. dtach does not try to attach to the newly created session, however, and exits instead.

dtach has a few options that allow you to modify its behavior. Each attaching process can have separate settings for these options, which allows for some flexibility.

-e <char>

Sets the detach character to <char>. When the detach character is pressed, dtach detaches itself from the current session and exits. The process running in the session is unaffected by the detach. By default, the detach character is set to ^\ (Ctrl-\).

-E

Disables the detach character. dtach does not try to scan input from the terminal for a detach character. The only way to detach from the session is then by sending the attaching process an appropriate signal.

-r <method>

Sets the redraw method to <method>. The valid methods are none, ctrl_l, or winch.

none disables redrawing completely, ctrl_l sends a Ctrl L character to the program if the terminal is in character-at-a-time and no-echo mode, and winch forces a WINCH signal to be sent to the program.

When creating a new session, the specified method is used as the default redraw method for the session. If not specified, the ctrl_l method is used.

-z

Disables processing of the suspend key. Normally, dtach will suspend itself when the suspend key is pressed. With this option, the suspend character is sent to the session instead of being handled by dtach.