What does the “first pid of a pane” in tmux mean

tmux

The entry in the tmux manpage's list of available variables for pane_pid reads as follows:

pane_pid PID of first process in pane

However, according to Run or send a command to a tmux pane in a running tmux session, "tmux does not supply a way to add extra processes to a pane once it has been started with its initial command."

So… what does it mean to return the PID of the first process of a pane? Is it reasonable to assume that this is the one and only PID of the pane, or is there actually some way for a pane to have multiple associated PIDs?

Best Answer

The PID returned by pane_pid is generally the PID of the command specified when opening the window (or the shell that was opened when no command was specified).

However, it is important to note that when specifying commands like top; bash -i, tmux prefixes the command with bash -c (i.e. the actual command executed when creating the pane is bash -c top; bash -i). In this case, the PID is that of the bash -c process, not of top.

In a sense, then, the "first process" of a pane is the one and only process of a pane, but it is not necessarily the process associated directly with the specified command.

Related Solutions

Tmux – What does bind-key -r mean

Quoting the TMUX(1) manpage:

The -r flag indicates this key may repeat, see the repeat-time option.

And a quick search for repeat-time yields this:

repeat-time time
Allow multiple commands to be entered without pressing the prefix-key again in the specified time milliseconds (the default is 500). Whether a key repeats may be set when it is bound using the -r flag to bind-key. Repeat is enabled for the default keys bound to the resize-pane command.

Linux – tmux: Detect which process runs in the active pane

Turns out tmux has powerful formatting capabilities for the list-panes command:

$ tmux list-panes -F '#{pane_active} #{pane_pid}'
0 4993
0 5382
1 6189

The command above will print

1 <process_pid>

for the active pane.

Fromatting options are described in man tmux:

 pane_active                     1 if active pane
 pane_pid                        PID of first process in pane

For the discussion of the term "first process in pane", see What does the "first pid of a pane" in tmux mean?

Best Answer

Related Solutions

Tmux – What does bind-key -r mean

Linux – tmux: Detect which process runs in the active pane

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