Emacs has a built-in way to save and restore sessions: the desktop.el library.As the Emacs manual says, putting this in the init file enables automatic save and restore of sessions:(desktop-save-mode 1)But, I wanted a different behavior:Automatically save the sessionBut don't restore it automaticallyI wanted to only use the session feature to restore sessions that I closed by mistake, or where I forgot to finish something before quitting Emacs. By default, I wanted a fresh session every time.But this also means that some session history has to be maintained; otherwise, a fresh session will start to write to the desktop file and then I will not be able to recover the old session.By default, the way to do this is to not set desktop-save-mode, but manually call desktop-save when needed, and then call desktop-read when needed. But, if I forget to save, I cannot restore.This elisp is what I came up with to make it work the way I want:(defvar my/desktop-snapshot-keep 5 "How many previous sessions to keep desktop snapshots for.")(defun my/desktop--snapshots () (nreverse (directory-files desktop-dirname t (concat "\\`" (regexp-quote desktop-base-file-name) "\\.[0-9]\\{8\\}T[0-9]\\{6\\}\\'"))))(defun my/desktop--take-snapshot () (let ((live (desktop-full-file-name))) (when (file-exists-p live) (let ((dest (concat live (format-time-string ".%Y%m%dT%H%M%S" (file-attribute-modification-time (file-attributes live)))))) (unless (file-exists-p dest) (copy-file live dest t t))))) (dolist (old (nthcdr my/desktop-snapshot-keep (my/desktop--snapshots))) (delete-file old)))(defun my/desktop--label (file) (format "%s %d buffers" (format-time-string "%Y-%m-%d %H:%M:%S" (file-attribute-modification-time (file-attributes file))) (with-temp-buffer (insert-file-contents file) (how-many "^(desktop-\\(?:create-buffer\\|append-buffer-args\\) " (point-min) (point-max)))))(add-hook 'emacs-startup-hook (lambda () (require 'desktop) (setq desktop-dirname (expand-file-name user-emacs-directory)) (my/desktop--take-snapshot) (desktop--get-file-modtime) (let ((owner (desktop-owner))) (unless (and owner (desktop--emacs-pid-running-p owner)) (desktop-claim-lock))) (desktop-save-mode 1)))(defun my/desktop-restore (file) "Restore the desktop snapshot FILE, prompting for one interactively." (interactive (progn (require 'desktop) (let* ((snapshots (or (my/desktop--snapshots) (user-error "No desktop snapshots in %s" desktop-dirname))) (choices (mapcar (lambda (f) (cons (my/desktop--label f) f)) snapshots))) (list (cdr (assoc (completing-read "Restore desktop session: " choices nil t) choices)))))) (desktop-release-lock) (let ((desktop-base-file-name (file-name-nondirectory file))) (desktop-read (file-name-directory file))) (desktop--get-file-modtime))Note that desktop-save-mode must not be enabled before after-init-hook fires, because that's where desktop.el decides to automatically restore. So, I enable it in emacs-startup-hook, which runs later. Other things inside my emacs-startup-hook lambda are workarounds for how desktop.el works, so they can be fragile if there are major changes to it.The lock check avoids a stale lock from a crashed Emacs silently disabling auto-save, and naming snapshots after the desktop file's mtime means restarting without saving anything doesn't use up one of the five slots.Here's what it looks like when I call my/desktop-restore:Of course, this can be made better by showing more information per session (like number of projects, names of last edited files or last visited buffers). Vertico/marginalia can show it nicely. Also maybe a section in emacs-dashboard to show recent sessions and click/enter to restore. Something for another day.