For years, tmux has been one of those tools many system administrators and developers install almost by reflex on any server. It keeps sessions alive after an SSH disconnection, lets users split the terminal into panes, work with multiple windows and return later to the same environment. Before that there was GNU Screen, still present on many Unix and Linux systems, and later came more minimalist options such as abduco or dtach.
Atch belongs to that same tradition, but with a different idea: it does not want to be a full terminal multiplexer or compete with tmux in window management. It wants to solve one specific need well: keep a process alive, allow the user to disconnect and reconnect, avoid breaking normal terminal behaviour and save the full history to disk. For anyone who only uses tmux to keep a process alive after an SSH drop, that difference may be enough.
The problem is not tmux, but using it for everything
tmux remains a very powerful tool. Its manual defines it as a terminal multiplexer that allows users to create, access and control several terminals from a single screen, with sessions that can be detached and reattached later. It also provides windows, panes, a status line, interactive commands and a server that manages sessions in the background.
That design is ideal for users who live inside tmux: they split panes, jump between windows, share sessions, customize shortcuts and build entire workflows around their configuration. The problem appears when tmux is used for something much smaller: launching a long-running job over SSH and recovering it later. In that case, many of its capabilities are unnecessary and some can get in the way.
Anyone who has struggled with mouse scrolling, copy mode, alternate screen buffers in programs such as vim, fzf or htop, TERM settings, true color or modern terminal sequences knows that multiplexers can introduce unexpected behaviour. It is not a random flaw: tmux has to interpret and manage the terminal because it provides panes, scrollback and windows. But that extra layer can also make an application behave differently inside and outside tmux.
Atch starts from the opposite premise. It does not implement a terminal emulator and does not try to reinterpret output. According to its repository, it passes the byte stream from the pseudoterminal to the user’s terminal without modifying it. That means mouse support, colors, OSC sequences, terminal graphics and programs using the alternate screen are handled by the user’s real terminal, not by an intermediate layer.
What atch adds compared with screen, tmux, abduco and dtach
GNU Screen was long the classic answer for keeping processes alive after a disconnection. The GNU Project describes it as a full-screen window manager that multiplexes a physical terminal between several processes, usually interactive shells, with independent windows, scrollback and detachable sessions.
abduco and dvtm split responsibilities more cleanly. abduco focuses on detaching and reattaching programs to a session, while dvtm provides dynamic window management in the console. Marc André Tanner, the author of both, presents abduco as a simpler and cleaner alternative to tmux or screen when combined with dvtm, and dvtm as a tiling window manager for the console that delegates session management to another tool.
atch sits closer to dtach and abduco than to tmux. Its goal is not to offer a desktop inside the terminal, but to create a named session, leave a process running, detach, reattach and preserve what happened. The main difference is persistent history: every byte written to the terminal is appended to a log file on disk under ~/.cache/atch/. When a session is reattached, atch first replays the full history and then hands over the live stream. That log survives disconnections, process exits, crashes and machine reboots until the user explicitly clears it.
| Tool | Approach | Strength | Limitation for some use cases |
|---|---|---|---|
| GNU Screen | Classic multiplexer | Widely available on many systems | Older behaviour and less comfortable configuration |
| tmux | Modern multiplexer | Windows, panes, sessions, ecosystem and scripting | Can be excessive if all you need is session persistence |
| abduco + dvtm | Unix-style separation of responsibilities | Simple sessions and console windowing as separate tools | Requires combining tools to get everything |
| dtach | Attach and detach processes | Extreme minimalism | No convenient listing or persistent on-disk history |
| atch | Transparent sessions with persistent logs | No terminal emulation and disk-backed output | No panes or window management |
atch also includes practical commands for automation. It can list sessions with atch list, send standard input to an already running session with atch push, follow the log with atch tail -f, kill a session with atch kill or clear history with atch clear. It can also show finished sessions that still have logs on disk via atch list -a.
Why it may interest sysadmins, DevOps teams and agent users
Atch is especially interesting in three scenarios. The first is classic remote administration: SSH into a machine, launch a build, migration, long copy, upgrade or maintenance task, disconnect and come back later. If the connection drops, the process should not die. If the process finishes while the user is away, the output should not be lost.
The second scenario is CI/CD and automation. A webhook can launch a deployment inside an atch session and return immediately. Later, an operator can attach to the session, review the complete history or follow the log without having been connected from the beginning. This does not replace a formal observability system or a deployment orchestrator, but it can be very useful in small environments, labs, personal servers or operational tasks where a lightweight tool fits better than a full platform.
The third case is AI agents and long-running model-assisted processes. Many current tools run tasks for minutes or hours: reviewing repositories, generating code, processing files, calling APIs, writing logs and waiting for instructions. Launching an agent inside a persistent session, disconnecting, coming back, reviewing everything it did and sending a new instruction via atch push can make atch a simple building block for experimental agentic AI workflows.
It also helps with basic operational forensics. If a process dies or the server reboots, the history does not disappear with an in-memory buffer. The repository notes that the log is capped at 1 MB by default, although it can be adjusted with the -C option or changed at compile time. That detail matters: saving everything to disk is valuable, but it also requires attention to size, privacy and rotation when used in environments that may expose sensitive data.
A small tool for users who do not need a full multiplexer
Atch is not a universal alternative to tmux. If someone lives in panes, layouts, windows, plugins, shared sessions and customized shortcuts, tmux will remain the better tool. Atch deliberately gives all of that up. Its proposal is to do fewer things, while reducing interference.
That choice makes sense within the Unix philosophy. Instead of assuming that every persistent session needs full multiplexing, atch separates the problem: keep a process alive, allow reattachment, record output and let the real terminal handle everything else. For many administrators, that simplicity may be more appealing than maintaining yet another configuration file in their dotfiles.
The project is written in C, builds with make and does not aim to depend on a heavy environment. Its adoption will depend on stability, distribution packaging, code auditing and community trust. Since it is a low-level tool that sits between terminal sessions, it is sensible to test it first in non-critical environments and review how it handles permissions, logs and session paths.
The arrival of atch is a reminder of something that is sometimes forgotten in the world of terminal tools: not every user needs more panes, more plugins or more layers. Sometimes they only need a command to keep running, the terminal to behave as usual and history not to vanish when it is needed most. For that specific case, atch offers a small, transparent and very Unix-like answer.
Frequently asked questions
Does atch replace tmux?
Not for everyone. It can replace tmux if you only use it to keep processes alive and return to a session later. It does not replace tmux panes, windows, plugins or advanced layout management.
How is atch different from dtach?
Atch follows a similar attach-and-detach philosophy, but adds persistent on-disk history, session listing, push for sending input to a session and commands such as tail, clear and kill.
Why does it matter that atch does not emulate a terminal?
Because it reduces the chance that mouse support, scrolling, colors, alternate screen behaviour or modern terminal sequences behave differently inside and outside the session.
Should users be careful with logs?
Yes. Atch saves output to disk by default. That is useful for recovering history, but it may include sensitive data. On shared servers or regulated environments, permissions, maximum size and cleanup policies should be reviewed.
source: administraciondesistemas