later

A background/delayed command execution tool for Linux and macOS.

I wrote later because I often need to run things in the background or schedule them for later, and at didn't quite fit my workflow. I wanted a tool that doesn't require a system daemon, and still lets me see and manage tasks throughout their lifecycle.

Demos

• Delay a task (e.g., pushing code after work hours so I don't forget)

  echo "git push origin main" | later 18:15

• Run commands in the background as I don't want to open a new terminal (check progress with later --log):

  $ later +0m # run commands immediately
  Execute at:  2026-02-13 18:55:56 (0s)
  Working dir: /Users/user/whatever/build
  later> cmake ..
  later> make -j`nproc`
  later> make install PREFIX=./install
  later>
  Task 1770976574_95743_a3f1 created

How it works

1. Each task's state is written only by its own daemon, a single-writer model.
2. There is no background daemon managing tasks; state is represented by files, and transitions are made atomic with open(O_EXCL) and rename(), which resists races and crashes.
3. A file lock (flock) tracks daemon liveness, and marker files represent a task's state.
4. Each task runs as a daemon (double fork, setsid, execl) and is managed through its process group, so cancelling reaches the whole command tree.
5. stdout/stderr are redirected to a log file, viewable anytime with --log.
6. Daemons are controlled through signals (cancel, pause/resume, purge).

Task lifecycle

    create               create --after/--require
       │                            │
       ▼                            ▼
  ┌─────────┐                  ┌─────────┐
  │ PENDING │                  │ WAITING │
  └─────────┘                  └─────────┘
       │                            │
       │ exec_at                    │ waited-for task ended
       └──────────────┬─────────────┘
                      ▼
                 ┌─────────┐    all ok     ┌───────────┐
                 │ RUNNING │ ────────────► │ COMPLETED │
                 └─────────┘               └───────────┘
                      │
                      │ a cmd fails        ┌────────┐
                      └──────────────────► │ FAILED │
                                           └────────┘

  From PENDING/WAITING/RUNNING:
       later --pause  ──► PAUSED (--resume returns to the previous state)

  From PENDING/WAITING/RUNNING/PAUSED:
       later --cancel ──► CANCELLED
       daemon dies    ──► FAILED (crash/OOM/kill)

  From WAITING with --require:
       the required task failed or was cancelled ──► FAILED

Differences from at

	later	at
Architecture	No background service, tasks stored as files	Centralized atd daemon
Output	later --log	Sent via system mail
Crash handling	Task file status and file lock	Lost if atd crashes
Cancellation	Cancel pending and running tasks	Cancel pending tasks only
Task visibility	Full lifecycle status (Running, Paused, Failed, ...)	Pending tasks only
Input	Pipe or interactive	Pipe or interactive
Extras	--retry, --pause/--resume, --after, --require, --clean, --purge	—

Examples

Background build with later

$ later +1m
Execute at:  2026-02-12 22:20:56 (1m)
Working dir: /Users/user/Downloads/build
later> cmake ../opencv-4.x
later> cmake --build build -j4
later>
Task 1770902509_74290_b1c2 created

Check task

$ later -l
    Status     Created at           Execute at           Cmds
1   running    2026-02-12 22:19:56  2026-02-12 22:20:56  3

View progress

$ later --log 1 | tail -3
[  6%] Linking C static library ../lib/libzlib.a
[  6%] Building C object 3rdparty/openjpeg/openjp2/CMakeFiles/libopenjp2.dir/mqc.c.o
[  6%] Built target zlib

Pause / resume a running task

$ later --pause 1
Task 1770902509_74290_b1c2 paused
$ later --resume 1
Task 1770902509_74290_b1c2 resumed

Cancel task

$ later --cancel 1
Task 1770902509_74290_b1c2 cancelled
$ later --log 1 | tail -3
make[2]: *** Waiting for unfinished jobs....
make: *** [all] Terminated: 15
Task cancelled by user.

Retry task

$ later --retry 1 +0s
Execute at:  2026-02-17 22:26:43 (0s)
Working dir: /Users/user/projects/build
Commands:
  1. cmake ../opencv-4.x
  2. cmake --build build -j4
Task 1771334803_35103_c9d0 created

Run a task after another task ends

$ later --after 2
Execute at:  after task 1771334803_35103_c9d0 ends
Working dir: /Users/user/projects/build
later> DESTDIR=./install cmake --install build
later>
Task 1770902571_74301_e5f7 created

Run a task after another task completes

$ later --require 3
Execute at:  requires task 1770902571_74301_e5f7 to complete
Working dir: /Users/user/projects/build
later> cmake --build build --target clean
later>
Task 1789715123_29892_1bf8 created

Dependencies

All third-party libraries are bundled in src/3rdparty. You only need a C11 compiler.

Library	Use
cofyc/argparse	command-line option parsing
antirez/linenoise	interactive line editing & completion

Uninstall

later --purge         # cancel every task and erase the data directory
rm ~/.local/bin/later # remove executable binary