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Session Management Commands

Perhaps the most useful feature of screen is the way it allows the user to move a session between terminals, by detaching and reattaching. This also makes life easier for modem users who have to deal with unexpected loss of carrier.

Detach

Command: autodetach state
(none)
Sets whether screen will automatically detach upon hangup, which saves all your running programs until they are resumed with a screen -r command. When turned off, a hangup signal will terminate screen and all the processes it contains. Autodetach is on by default.

Command: detach
(C-a d, C-a C-d)
Detach the screen session (disconnect it from the terminal and put it into the background). A detached screen can be resumed by invoking screen with the -r option (see section Invoking Screen). The -h option tells screen to immediately close the connection to the terminal (`hangup').

Command: password [crypted_pw]
(none)
Present a crypted password in your `.screenrc' file and screen will ask for it, whenever someone attempts to resume a detached session. This is useful, if you have privileged programs running under screen and you want to protect your session from reattach attempts by users that managed to assume your uid. (I.e. any superuser.) If no crypted password is specified, screen prompts twice a password and places its encryption in the paste buffer. Default is `none', which disables password checking.

Power Detach

Command: pow_detach
(C-a D D)
Mainly the same as detach, but also sends a HANGUP signal to the parent process of screen.
Caution: This will result in a logout if screen was started from your login shell.

Command: pow_detach_msg [message]
(none)
The message specified here is output whenever a power detach is performed. It may be used as a replacement for a logout message or to reset baud rate, etc. Without parameter, the current message is shown.

Lock

Command: lockscreen
(C-a x, C-a C-x)
Call a screenlock program (`/local/bin/lck' or `/usr/bin/lock' or a builtin, if no other is available). Screen does not accept any command keys until this program terminates. Meanwhile processes in the windows may continue, as the windows are in the detached state. The screenlock program may be changed through the environment variable $LOCKPRG (which must be set in the shell from which screen is started) and is executed with the user's uid and gid.

Warning: When you leave other shells unlocked and have no password set on screen, the lock is void: One could easily re-attach from an unlocked shell. This feature should rather be called lockterminal.

Multiuser Session

These commands allow other users to gain access to one single screen session. When attaching to a multiuser screen the sessionname is specified as username/sessionname to the -S command line option. Screen must be compiled with multiuser support to enable features described here.

Multiuser

Command: multiuser state
(none)
Switch between single-user and multi-user mode. Standard screen operation is single-user. In multi-user mode the commands acladd, aclchg and acldel can be used to enable (and disable) other users accessing this screen.

Acladd

Command: acladd usernames
Command: addacl usernames
(none)
Enable users to fully access this screen session. Usernames can be one user or a comma separated list of users. This command enables to attach to the screen session and performs the equivalent of aclchg usernames +rwx "#?". To add a user with restricted access, use the aclchg command below. Addacl is a synonym to acladd. Multi-user mode only.

Aclchg

Command: aclchg usernames permbits list
Command: chacl usernames permbits list
(none)
Change permissions for a comma separated list of users. Permission bits are represented as `r', `w' and `x'. Prefixing `+' grants the permission, `-' removes it. The third parameter is a comma separated list of commands or windows (specified either by number or title). The special list `#' refers to all windows, `?' to all commands. If usernames consists of a single `*', all known users are affected. A command can be executed when the user has the `x' bit for it. The user can type input to a window when he has its `w' bit set and no other user obtains a writelock for this window. Other bits are currently ignored. To withdraw the writelock from another user in e.g. window 2: `aclchg username -w+w 2'. To allow read-only access to the session: `aclchg username -w "#"'. As soon as a user's name is known to screen, he can attach to the session and (per default) has full permissions for all command and windows. Execution permission for the acl commands, at and others should also be removed or the user may be able to regain write permission. Chacl is a synonym to aclchg. Multi-user mode only.

Acldel

Command: acldel username
(none)
Remove a user from screen's access control list. If currently attached, all the user's displays are detached from the session. He cannot attach again. Multi-user mode only.

Aclgrp

Command: aclgrp username [groupname]
(none)
Creates groups of users that share common access rights. The name of the group is the username of the group leader. Each member of the group inherits the permissions that are granted to the group leader. That means, if a user fails an access check, another check is made for the group leader. A user is removed from all groups the special value `none' is used for groupname. If the second parameter is omitted all groups the user is in are listed.

Displays

Command: displays
(C-a *)
Shows a tabular listing of all currently connected user front-ends (displays). This is most useful for multiuser sessions.

aclumask

Command: aclumask [users]+/-bits ...
Command: umask [users]+/-bits ...
(none)
This specifies the access other users have to windows that will be created by the caller of the command. Users may be no, one or a comma separated list of known usernames. If no users are specified, a list of all currently known users is assumed. Bits is any combination of access control bits allowed defined with the aclchg command. The special username `?' predefines the access that not yet known users will be granted to any window initially. The special username `??' predefines the access that not yet known users are granted to any command. Rights of the special username nobody cannot be changed (see the su command). Umask is a synonym to aclumask.

Wall

Command: wall message
(none)
Write a message to all displays. The message will appear in the terminal's status line.

Writelock

Command: writelock on|off|auto
(none)
In addition to access control lists, not all users may be able to write to the same window at once. Per default, writelock is in `auto' mode and grants exclusive input permission to the user who is the first to switch to the particular window. When he leaves the window, other users may obtain the writelock (automatically). The writelock of the current window is disabled by the command writelock off. If the user issues the command writelock on he keeps the exclusive write permission while switching to other windows.

Command: defwritelock on|off|auto
(none)
Sets the default writelock behavior for new windows. Initially all windows will be created with no writelocks.

Su

Command: su [username [password [password2]]]
(none)
Substitute the user of a display. The command prompts for all parameters that are omitted. If passwords are specified as parameters, they have to be specified un-crypted. The first password is matched against the systems passwd database, the second password is matched against the screen password as set with the commands acladd or password. Su may be useful for the screen administrator to test multiuser setups. When the identification fails, the user has access to the commands available for user `nobody'. These are detach, license, version, help and displays.

Session Name

Command: sessionname [name]
(none)
Rename the current session. Note that for screen -list the name shows up with the process-id prepended. If the argument name is omitted, the name of this session is displayed.
Caution: The $STY environment variable still reflects the old name. This may result in confusion. The default is constructed from the tty and host names.

Suspend

Command: suspend
(C-a z, C-a C-z)
Suspend screen. The windows are in the detached state while screen is suspended. This feature relies on the parent shell being able to do job control.

Quit

Command: quit
(C-a C-\)
Kill all windows and terminate screen. Note that on VT100-style terminals the keys C-4 and C-\ are identical. So be careful not to type C-a C-4 when selecting window no. 4. Use the empty bind command (as in bind "^\") to remove a key binding (see section Key Binding).

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