Terminal Multiplexers: Screen, Tmux

command line options | key bindings | customization | terminology | documentation

Command Line Options

screen tmux create session and attach $ screen $ tmux create session foo and attach $ screen -S foo $ tmux new -s foo create detached session foo $ screen -S foo -d -m $ tmux new -s foo -d list sessions $ screen -list $ tmux ls attach $ screen -r $ tmux attach attach to session foo $ screen -r foo $ tmux attach -t foo attach to session by pid $ screen -r pid kill session foo $ screen -r foo -X quit $ tmux kill-session -t foo send multiplexer command to session foo $ screen -r foo -X command $ tmux command -t foo run ls in session foo $ screen -r foo -X stuff "ls $(echo -ne '\015')" $ tmux send-keys -t foo 'ls' C-m run vi in new window $ screen vi /etc/motd $ tmux new-window vi /etc/motd

Key Bindings

sessions | windows | regions | panes | paste buffer | copy mode

screen tmux C-a cmd command C-b cmd command help ? :help ? :list-keys send prefix to app a :meta C-b :send-prefix suspend multiplexer C-z :suspend C-z :suspend-client show previous multiplexer message m

C-m :lastmsg ~ :show-messages source file :source file :source-file file detach d

C-d :detach d :detach-client sessions screen tmux C-a cmd command C-b cmd command new session :new new named session :new -s foo switch session s :choose-session rename session :sessionname foo $ command-prompt -I #S "rename-session '%%'" kill session C-\ :quit windows screen tmux C-a cmd command C-b cmd command create new window c

C-c :screen c :new-window switch to next window n

C-n

SPACE :next n :next-window switch to previous window BACKSPACE

h

p

C-p :prev p :previous-window toggle to last window C-a :other select window n n :select-window -t : n list windows w

C-w :windows :list-windows show current window number and name N :number renumber current window . position :move-window move current window to another session . sessname

. sessnum : position redraw current window l

C-l :redisplay r :refresh-client choose window interactively " :windowlist -b w :choose-window rename window A :title , select window foo ' :select f foo close current window C-k :kill & :kill-window join window 1 to current window :join-pane -s 1 join region 0 of window 1 to current window :join-pane -s 1.0 regions screen tmux C-a cmd command C-b cmd command split into top and bottom regions S :split move down to next region TAB :focus make regions same height :resize = close current region X :remove close all but current region Q :only clear current region C :clear log region to file file is screenlog.NN

:log turn off logging :log off make current region n rows taller/shorter :resize + n

:resize - n make current region n rows tall :resize n panes screen tmux C-a cmd command C-b cmd command split into left and right panes % :split-window -h split into top and bottom panes " :split-window switch to next panes o :select-pane rotate panes C-o :rotate-window reverse rotate panes M-o :rotate-window -D arrange panes side-by-side and same width M-1 arrange panes stacked and same height M-2 swap current and previous pane { :swap-pane -U swap current and next pane } :swap-pane -D change arrangement of panes SPACE :next-layout close current pane x :confirm-before kill-pane break current pane into separate window ! :break-pane list panes :list-panes display pane numbers q :display-panes clear current pane :clear-history log pane to file :pipe-pane "cat > /tmp/tmux.log" turn off logging :pipe-pane resize pane left/up n cells :resize-pane -L n

:resize-pane -U n paste buffer screen tmux C-a cmd command C-b cmd command enter copy mode [

C-[

ESC :copy [ :copy-mode paste most recent buffer ] ] :paste-buffer list buffers only one buffer # :list-buffers choose buffer to paste interactively = :choose-buffer write buffer to file writes to /tmp/screen-exchange:

> :writebuf path :save-buffer path copy file to buffer copies from /tmp/screen-exchange:

< :readbuf path :load-buffer path copy mode screen tmux cmd command cmd command default bindings Vim-style Emacs-style set mark SPACE C-SPACE copy from mark to point and exit copy mode when mark is set:

SPACE C-w single column movement also left right arrow

h l also left right arrow

C-b C-h single line movement also down up arrow

j k also down up arrow

C-n C-p beginning of line 0 C-a end of line $ C-e forward word e M-f backward word b M-b page up C-b M-v page down C-f C-v beginning of buffer g M-< end of buffer G M-> search backwards ? phrase C-r phrase search forwards / phrase C-s phrase exit copy mode any unbound key also works:

ESC q

Customization

screen tmux startup file ~/.screenrc ~/.tmux.conf scrollback length defscrollback 2000 set-option history-limit 2000 set prefix how to set prefix to C-b, with a second C-b to send a C-b to the controlling process:

escape ^B^B set-option -g prefix C-a define key binding bind bind-key undefine key binding unbind-key set copy/scrollback key binding style vi bindings by default.

When redefining, use vi

commands on left of equations:

markkeys h=^B:l=^F:$=^E emacs by default:

setw -g mode-keys vi disable startup message startup_message off number windows from one 0 by default:

set -g base-index 1 always show status bar splitonly by default:

caption always

caption splitonly on by default:

set-option status off

set-option status on customize caption caption string " string " set-option status-left " string "

set-option status-right string

caption escapes screen tmux shell output first arg is an identifier referenced by the caption string;

the second and third argument set the refresh in seconds



backtick 1 60 60 cmd

caption always "%1 ` " #( cmd ) date (YYYYMMDD) %Y%m%d month name %M weekday name %D 24 hr time %C 12 hr time %c%A color %{ry} red text, yellow background %{dd}foo #[fg=red,bg=yellow] red text, yellow background #[default] fully qualified hostname #H hostname %H #h session name %S added in 4.1 #S current window flag %F #F current window index %n #I current pane index none #P current pane title none #T window name %t #W literal % or # %% ##

Terminology

server | client | session | window | region | pane

how ssh works:

When a user logs in to a remote host using ssh , the ssh process contacts an sshd process listening on TCP port 22. The sshd process opens up a new TCP port and forks off a copy of itself for communicating with the ssh process. The new port and child process are for the exclusive use of the connection being established.

The child sshd process authenticates the ssh process, and if it passes it creates a pseudo-terminal. It then forks the remote user's shell which becomes the controlling process for the pseudo-terminal.

If the network connection is closed, either explicitly by the ssh process or because of a loss of network connectivity, the child sshd process closes the pseudo-terminal, and this in turn causes the shell to exit.

the SIGHUP problem:

If the shell had any process groups running when it exits, they are sent a SIGHUP signal followed by a SIGCONT signal. By default processes exit when they receive SIGHUP . This makes it challenging to run long-running jobs on a remote host when the network connection is unreliable.

A simple solution to the SIGHUP problem is to run each job with nohup . Optionally, shells such as bash and zsh have a disown built-in which can be used on a process that is already running, should the user have neglected to run it with nohup .

The fish shell when invoking a process in the background with & sets the signal handling state of the process to ignore SIGHUP . It will do the same if the process is suspended with ^Z and then put in the background with bg .

Multiplexers offer a solution which protects the shell instead of the job. The user doesn't need to remember to run each job with nohup . As an added benefit any state kept by the shell is preserved.

server:

The multiplexer server creates pseudo-terminals which are used for running and interacting with programs.

Screen and Tmux servers can create multiple pseudo-terminals. The controlling process for each pseudo-terminal is the user's shell.

client:

To see the output of a shell the user must connect to the multiplexer server with a multiplexer client process.

If the multiplexer is being run on a remote machine and the user's connection is lost, the server and its terminals and controlling processes persist, but the client process exits.

When multiple client processes connect to the same server they see the same output. This is a way to share a display across computers.

session:

Multiplexers support multiple sessions. Each multiplexer session has its own set of terminals and controlling processes which it is running. The client must choose a session to attach to, and will only be able to see the output of the controlling processes in that session. Sessions can be given names to make it easy for the client to choose the correct session.

Screen launches a separate server process for each session. Screen servers and clients communicate via named pipes.

Tmux by default will only run one server process per user, and this server process can have multiple sessions. A Tmux client and the server communicate via a Unix domain socket in the /tmp directory. The -L option can be used to specify a different socket; a new server is created for each socket.

window:

Both Screen and Tmux have entities which they call windows.

A Screen window has a single pseudo-terminal and shell. A Tmux window can have multiple pseudo-terminals and shells.

Screen windows can share the viewport. The Tmux viewport can only display one window at a time.

Both Screen and Tmux windows are numbered starting from zero.

region:

Screen can divide the viewport into multiple regions.

Screen regions can be empty or they can contain a window. The same window can be displayed in more than one region. When regions share a window their content is identical.

Screen regions are stacked on top of each other and extend the full width of the window.

pane:

Tmux can divide windows into multiple panes.

Tmux panes contain a single pseudo-terminal with a shell, and each pseudo-terminal and shell belongs to only one pane.

Tmux windows can be divided both horizontally and vertically into panes. Each division can be subdivided further.

Tmux panes are numbered.

Tmux panes can be moved between windows.

command character (prefix):

Multiplexers pass most input on to the shell in the region with focus, but a special command character is used to send commands to the multiplexer.

The default command character in Screen is C-a . The keystrokes which follow C-a are interpreted by Screen instead of being passed to the shell.

Tmux calls the command character the prefix and the default value is C-b . The keystrokes following the prefix are interpreted by Tmux instead of being passed to shell.

scrollback buffer (history):

Screen and Tmux keep a history of the output of each shell. The maximum length of the output in lines is configurable.

Screen calls the history the scrollback buffer.

copy/scrollback mode (copy mode):

Screen and Tmux support two modes for each region. In default mode, input which is not intercepted by the multiplexer is passed to the shell.

When the region is in copy mode the region behaves like a read-only buffer of an editor. The contents are the output of the shell including output that may have scrolled off the top of the region.

The keybindings used by Screen in copy/scrollback mode are Vim-style. It is possible to customize them to be Emacs-style.

The Tmux calls copy/scrollback mode simply copy mode. The keybindings are by default Emacs-style.

paste buffer:

Screen has a single paste buffer.

Tmux has multiple paste buffers. The Tmux paste buffers are numbered; the most recent is number zero. Sessions share a common paste buffer history.

caption (status line):

When a Screen window is split into multiple regions, a caption line is placed at the bottom of each region. When a window contains a single region, Screen by default does not display a caption. The caption, when present, contains information from Screen. The information that is displayed can be customized.

Tmux calls the line at the bottom of a window the status line. By default it is always displayed, though it can be turned off. The status line contains information from Tmux which can be customized.