24.4 Killing Buffers

If you continue an Emacs session for a while, you may accumulate a large number of buffers. You may then find it convenient to kill the buffers you no longer need. On most operating systems, killing a buffer releases its space back to the operating system so that other programs can use it. Here are some commands for killing buffers:

C-x k bufname <RET>

Kill buffer bufname (kill-buffer).

M-x kill-some-buffers

Offer to kill each buffer, one by one.

C-x k (kill-buffer) kills one buffer, whose name you specify in the minibuffer. The default, used if you type just <RET> in the minibuffer, is to kill the current buffer. If you kill the current buffer, another buffer becomes current: one that was current in the recent past but is not displayed in any window now. If you ask to kill a file-visiting buffer that is modified (has unsaved editing), then you must confirm with yes before the buffer is killed.

The command M-x kill-some-buffers asks about each buffer, one by one. An answer of y means to kill the buffer. Killing the current buffer or a buffer containing unsaved changes selects a new buffer or asks for confirmation just like kill-buffer.

The buffer menu feature (see Several Buffers) is also convenient for killing various buffers.

If you want to do something special every time a buffer is killed, you can add hook functions to the hook kill-buffer-hook (see Hooks).

If you run one Emacs session for a period of days, as many people do, it can fill up with buffers that you used several days ago. The command M-x clean-buffer-list is a convenient way to purge them; it kills all the unmodified buffers that you have not used for a long time. An ordinary buffer is killed if it has not been displayed for three days; however, you can specify certain buffers that should never be killed automatically, and others that should be killed if they have been unused for a mere hour.

You can also have this buffer purging done for you, every day at midnight, by enabling Midnight mode. Midnight mode operates each day at midnight; at that time, it runs clean-buffer-list, or whichever functions you have placed in the normal hook midnight-hook (see Hooks).

To enable Midnight mode, use the Customization buffer to set the variable midnight-mode to t. See Easy Customization.