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Use umux spawn to start a shell or application, then wait for a task-specific readiness signal with a timeout. A live session preserves shell state between commands; optional JSONL logs preserve input and output history, not a running process. Use umux rm to remove a session, but the project documentation does not say whether that also removes its log files.
These instructions describe the documented behavior of umux. Its GitHub repository was archived and made read-only on July 6, 2026, so check that the package is still available before attempting a fresh installation.
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Install umux and start a session
The project README lists Node.js 20 or later and Linux, macOS, or Windows with WSL as requirements. It gives this global npm installation command:
npm install -g @combinatrix-ai/umuxBecause the repository is archived, package availability and compatibility with your environment may have changed. If installation succeeds, start a basic Bash session with:
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umux spawn bashFor an application, give the session a name and wait until its screen displays a distinctive phrase. The README demonstrates launching Claude this way:
umux spawn -n claude claude
--block-until-screen-match "Welcome"
--timeout 30000Choose a phrase that actually signals readiness for your task; a screen match only establishes that the specified text appeared, not that every subsequent action will succeed.
Choose a bounded readiness condition
When startup timing matters, wait for a signal that reflects what you need to do next. The documented options include waiting for a shell to become ready, matching output, matching visible screen content, or waiting until output is idle. Every wait needs a timeout, either supplied to the command or configured with UMUX_DEFAULT_TIMEOUT. The README describes this as preventing infinite hangs; treat it as the project’s documented behavior.
| What you need to detect | Documented wait approach | When it fits |
|---|---|---|
| A usable shell prompt | umux wait --block-until-ready --timeout 60000 |
When the next action is a shell command. |
| A known string in command output | Wait for an output match with a timeout. | When a command prints a distinctive completion or status line. |
| A phrase visible in a terminal interface | Wait for a screen match with a timeout. | When starting a TUI or other interactive application. |
| Output to stop changing | Wait until output is idle with a timeout. | When a quiet period is a useful signal, rather than a specific phrase. |
The README does not prescribe one universal timeout. Set a limit appropriate to the startup task, and avoid unbounded waits. For application startup, choose a timeout long enough for normal initialization but short enough that a failed launch does not leave automation waiting indefinitely.
Understand what persists
State within a live shell
A live umux shell keeps state across commands in that session. The README illustrates changing directories, exporting an environment variable, and sourcing a file in separate commands; it describes the working directory, environment variables, and aliases as preserved. This is session continuity, not a promise that the session will survive a host restart.
Queryable in-memory history
The umux logs command can show session I/O history held in memory. By default, it displays the last 100 lines; the README also documents --tail, --all, and --search options. This is useful for inspecting recent activity, but it should not be confused with durable storage.
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Optional JSONL disk logs
To write session input and output to disk, set UMUX_LOG_DIR to the directory for logs. The README says umux appends JSONL records to a dated, session-named file. For example, set the variable in the environment before launching umux; use the syntax for your shell:
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export UMUX_LOG_DIR="$HOME/umux-logs"
# PowerShell
$env:UMUX_LOG_DIR = "$HOME/umux-logs"Logs may contain sensitive data. If commands could include credentials or private information, disable input logging with UMUX_LOG_INPUT=0 before starting the session. The README does not specify log encryption, retention, or whether removing a session deletes its JSONL files, so do not assume those protections or cleanup behaviors.
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Disk logs preserve a record of I/O; the documentation does not claim that they restore a shell or its running process after a host restart.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Remove a session when finished
The README’s quick-start sequence ends with umux rm. Its CLI reference describes rm as removing a session and kill as killing the session process. Use the documented removal command when you are done:
umux rmDo not infer from session removal that saved JSONL logs are erased. The README does not clarify whether umux rm or umux kill deletes those files.
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The umux README reports an example comparison of 61 lines with tmux versus 35 with umux, and median runtimes of 6.68 seconds versus 5.58 seconds, with the median based on 10 runs. These are figures reported by the project author for that example, not an independent study or a general benchmark for other workloads.
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