# libtmux.core/new-session!

- **Module:** libtmux.core
- **Package:** io.github.libtmux:libtmux-clojure
- **Language:** Clojure
- **Kind:** function
- **Source:** https://github.com/libtmux/libtmux-java/blob/5f88402151ff08fc0390dd438b90963692ec3fe4/libtmux-clojure/src/main/clojure/libtmux/core.clj#L242
- **Public owner:** libtmux.core
- **Page:** https://libtmux.org/en/clojure/latest/reference/libtmux-core-new-session/

```
(new-session! server options)
```

Creates a detached session and returns a fresh captured session map.

Options are `:name`, `:window-name`, `:command` (nonempty argv vector), `:directory`
(path), and `:environment` (string keys and values). Unknown keys are rejected.
A recapture failure can occur after creation; inspect [[error-summary]] before
retrying a mutation.

## Examples

Create a session running cat. Use JDK 25 or newer, the Clojure CLI, Git and tmux on Linux or macOS, with /bin/cat and /bin/sh available. These packages are unpublished. In an empty directory, install this exact source into the consumer's isolated Maven repository:

```console
$ git clone https://github.com/libtmux/libtmux-java libtmux-source && \
  git -C libtmux-source checkout --detach 5f88402151ff08fc0390dd438b90963692ec3fe4 && \
  (cd libtmux-source && ./gradlew \
    :libtmux:publishToMavenLocal \
    :libtmux-clojure:publishToMavenLocal \
    --console=plain \
    "-Dmaven.repo.local=$PWD/../m2")
```

Save this file as `deps.edn`. Dependencies resolve from the isolated m2 directory; the core.async dependency is only enabled by its alias.

[Source example](https://github.com/libtmux/libtmux-java/blob/5f88402151ff08fc0390dd438b90963692ec3fe4/examples/api/clojure/deps.edn).

```clojure
{:paths ["src/main/clojure"]
 :mvn/local-repo "m2"
 :deps {org.clojure/clojure {:mvn/version "1.12.6"}
        io.github.libtmux/libtmux-clojure {:mvn/version "0.1.2-SNAPSHOT"}}
 :aliases
 {:core-async
  {:extra-deps
   {io.github.libtmux/libtmux-clojure-core-async {:mvn/version "0.1.2-SNAPSHOT"}}}}}
```

Save this file as `run.sh`. The launcher creates and stops a private server, including after program failure, and reports leaked servers as errors.

[Source example](https://github.com/libtmux/libtmux-java/blob/5f88402151ff08fc0390dd438b90963692ec3fe4/examples/api/run.sh).

```sh
#!/bin/sh
set -eu

if [ "$#" -eq 0 ]; then
    printf 'Usage: sh run.sh program [arguments...]\n' >&2
    exit 2
fi
binary=$(command -v "${TMUX_BIN:-tmux}")
root=${API_RUN_ROOT:-/tmp/libtmux-java-dev}

# A client that names no socket follows TMUX or LIBTMUX_SOCKET*, and otherwise lands on the default
# socket under TMUX_TMPDIR. The program gets none of them, and a TMUX_TMPDIR of its own below.
unset TMUX TMUX_PANE
for name in $(env | sed -n 's/^\(LIBTMUX_SOCKET[A-Za-z0-9_]*\)=.*/\1/p'); do
    unset "$name"
done

mkdir -p "$root"
directory=$(mktemp -d "$root/api.XXXXXX")
tmpdir=$(mktemp -d "$root/tmpdir.XXXXXX")
socket="$directory/tmux.sock"
config="$directory/tmux.conf"

serves() {
    "$binary" -S "$1" display-message -p '#{pid}' >/dev/null 2>&1
}

# Stops the server on the socket, then waits for it to stop answering.
stop() {
    "$binary" -S "$1" kill-server || return 1
    attempts=0
    while serves "$1" && [ "$attempts" -lt 60 ]; do
        sleep 0.05
        attempts=$((attempts + 1))
    done
    ! serves "$1"
}

cleanup() {
    status=$?
    trap - 0 HUP INT TERM PIPE
    # A closed output must not end the cleanup, whose messages are the only thing left to write.
    trap '' PIPE
    set +e
    stuck=
    left=
    if [ -S "$socket" ] && serves "$socket" && ! stop "$socket"; then
        stuck="$stuck tmux.sock"
    fi
    # Every socket anywhere under either directory, without following links. Only one a server answers
    # on is a leak; the runner's own is expected to be there.
    old_ifs=$IFS
    IFS='
'
    set -f
    for candidate in $(find "$tmpdir" "$directory" -type s 2>/dev/null); do
        [ "$candidate" = "$socket" ] && continue
        serves "$candidate" || continue
        case "$candidate" in
            "$tmpdir"/*) name=${candidate#"$tmpdir"/} ;;
            *) name=${candidate#"$directory"/} ;;
        esac
        left="$left $name"
        stop "$candidate" || stuck="$stuck $name"
    done
    set +f
    IFS=$old_ifs
    if [ -n "$stuck" ]; then
        printf 'tmux still answers on%s after kill-server; kept %s and %s under the runner root\n' \
            "$stuck" "${directory##*/}" "${tmpdir##*/}" >&2
        exit 1
    fi
    rm -rf "$directory" "$tmpdir" || exit 1
    if [ -n "$left" ]; then
        printf 'The program left a tmux server running:%s\n' "$left" >&2
        exit 1
    fi
    exit "$status"
}
trap cleanup 0
trap 'exit 1' HUP INT TERM PIPE

# A default socket path longer than this does not fit in sun_path.
default_socket="$tmpdir/tmux-$(id -u)/default"
if [ "$(printf '%s' "$default_socket" | wc -c)" -gt 100 ]; then
    printf 'API_RUN_ROOT is too long for a tmux socket\n' >&2
    exit 1
fi
TMUX_TMPDIR=$tmpdir
export TMUX_TMPDIR

printf 'set-option -g default-shell /bin/sh\n' > "$config"
"$binary" -S "$socket" -f "$config" new-session -d -s work-one -n editor /bin/cat
"$binary" -S "$socket" split-window -h -t '=work-one:editor' /bin/cat
"$binary" -S "$socket" new-window -d -t '=work-one' -n logs /bin/cat
"$binary" -S "$socket" new-session -d -s work-two -n editor /bin/cat
"$@" "$binary" "$socket" "$config"
"$binary" -S "$socket" has-session -t '=work-one'
"$binary" -S "$socket" has-session -t '=work-two'
```

Save the complete program as `src/main/clojure/libtmux/examples/api/new_session.clj`, creating its parent directories. Closing its client leaves the launcher's server running.

[Source example](https://github.com/libtmux/libtmux-java/blob/5f88402151ff08fc0390dd438b90963692ec3fe4/examples/src/main/clojure/libtmux/examples/api/new_session.clj).

```clojure
(ns libtmux.examples.api.new-session
  "Create a session running cat and inspect the replacement observation."
  (:require [libtmux.core :as tm]))

(defn -main [& args]
  (when-not (= 3 (count args))
    (throw (IllegalArgumentException. "expected: tmux-binary socket-path config-file")))
  (let [[binary socket config] args]
    (with-open [server (tm/open! {:binary binary :socket-path socket
                                 :config-file config})]
      (let [session (tm/new-session! server {:name "api-session" :command ["/bin/cat"]})]
        (assert (= "api-session" (:session/name session)))
        (println (str "created=" (:session/name session)))))))
```

Run it with the private fixture. Set TMUX_BIN to select another tmux binary:

```console
$ sh run.sh clojure \
  -J-Dclojure.main.report=stderr \
  -M \
  -m libtmux.examples.api.new-session
```

Expected output:

```text
created=api-session
```

Use a preserved Java Pane ref to read a command exit status and output. Use JDK 25 or newer, the Clojure CLI, Git and tmux on Linux or macOS, with /bin/cat and /bin/sh available. These packages are unpublished. In an empty directory, install this exact source into the consumer's isolated Maven repository:

```console
$ git clone https://github.com/libtmux/libtmux-java libtmux-source && \
  git -C libtmux-source checkout --detach 5f88402151ff08fc0390dd438b90963692ec3fe4 && \
  (cd libtmux-source && ./gradlew \
    :libtmux:publishToMavenLocal \
    :libtmux-clojure:publishToMavenLocal \
    --console=plain \
    "-Dmaven.repo.local=$PWD/../m2")
```

Save this file as `deps.edn`. Dependencies resolve from the isolated m2 directory; the core.async dependency is only enabled by its alias.

[Source example](https://github.com/libtmux/libtmux-java/blob/5f88402151ff08fc0390dd438b90963692ec3fe4/examples/api/clojure/deps.edn).

```clojure
{:paths ["src/main/clojure"]
 :mvn/local-repo "m2"
 :deps {org.clojure/clojure {:mvn/version "1.12.6"}
        io.github.libtmux/libtmux-clojure {:mvn/version "0.1.2-SNAPSHOT"}}
 :aliases
 {:core-async
  {:extra-deps
   {io.github.libtmux/libtmux-clojure-core-async {:mvn/version "0.1.2-SNAPSHOT"}}}}}
```

Save this file as `run.sh`. The launcher creates and stops a private server, including after program failure, and reports leaked servers as errors.

[Source example](https://github.com/libtmux/libtmux-java/blob/5f88402151ff08fc0390dd438b90963692ec3fe4/examples/api/run.sh).

```sh
#!/bin/sh
set -eu

if [ "$#" -eq 0 ]; then
    printf 'Usage: sh run.sh program [arguments...]\n' >&2
    exit 2
fi
binary=$(command -v "${TMUX_BIN:-tmux}")
root=${API_RUN_ROOT:-/tmp/libtmux-java-dev}

# A client that names no socket follows TMUX or LIBTMUX_SOCKET*, and otherwise lands on the default
# socket under TMUX_TMPDIR. The program gets none of them, and a TMUX_TMPDIR of its own below.
unset TMUX TMUX_PANE
for name in $(env | sed -n 's/^\(LIBTMUX_SOCKET[A-Za-z0-9_]*\)=.*/\1/p'); do
    unset "$name"
done

mkdir -p "$root"
directory=$(mktemp -d "$root/api.XXXXXX")
tmpdir=$(mktemp -d "$root/tmpdir.XXXXXX")
socket="$directory/tmux.sock"
config="$directory/tmux.conf"

serves() {
    "$binary" -S "$1" display-message -p '#{pid}' >/dev/null 2>&1
}

# Stops the server on the socket, then waits for it to stop answering.
stop() {
    "$binary" -S "$1" kill-server || return 1
    attempts=0
    while serves "$1" && [ "$attempts" -lt 60 ]; do
        sleep 0.05
        attempts=$((attempts + 1))
    done
    ! serves "$1"
}

cleanup() {
    status=$?
    trap - 0 HUP INT TERM PIPE
    # A closed output must not end the cleanup, whose messages are the only thing left to write.
    trap '' PIPE
    set +e
    stuck=
    left=
    if [ -S "$socket" ] && serves "$socket" && ! stop "$socket"; then
        stuck="$stuck tmux.sock"
    fi
    # Every socket anywhere under either directory, without following links. Only one a server answers
    # on is a leak; the runner's own is expected to be there.
    old_ifs=$IFS
    IFS='
'
    set -f
    for candidate in $(find "$tmpdir" "$directory" -type s 2>/dev/null); do
        [ "$candidate" = "$socket" ] && continue
        serves "$candidate" || continue
        case "$candidate" in
            "$tmpdir"/*) name=${candidate#"$tmpdir"/} ;;
            *) name=${candidate#"$directory"/} ;;
        esac
        left="$left $name"
        stop "$candidate" || stuck="$stuck $name"
    done
    set +f
    IFS=$old_ifs
    if [ -n "$stuck" ]; then
        printf 'tmux still answers on%s after kill-server; kept %s and %s under the runner root\n' \
            "$stuck" "${directory##*/}" "${tmpdir##*/}" >&2
        exit 1
    fi
    rm -rf "$directory" "$tmpdir" || exit 1
    if [ -n "$left" ]; then
        printf 'The program left a tmux server running:%s\n' "$left" >&2
        exit 1
    fi
    exit "$status"
}
trap cleanup 0
trap 'exit 1' HUP INT TERM PIPE

# A default socket path longer than this does not fit in sun_path.
default_socket="$tmpdir/tmux-$(id -u)/default"
if [ "$(printf '%s' "$default_socket" | wc -c)" -gt 100 ]; then
    printf 'API_RUN_ROOT is too long for a tmux socket\n' >&2
    exit 1
fi
TMUX_TMPDIR=$tmpdir
export TMUX_TMPDIR

printf 'set-option -g default-shell /bin/sh\n' > "$config"
"$binary" -S "$socket" -f "$config" new-session -d -s work-one -n editor /bin/cat
"$binary" -S "$socket" split-window -h -t '=work-one:editor' /bin/cat
"$binary" -S "$socket" new-window -d -t '=work-one' -n logs /bin/cat
"$binary" -S "$socket" new-session -d -s work-two -n editor /bin/cat
"$@" "$binary" "$socket" "$config"
"$binary" -S "$socket" has-session -t '=work-one'
"$binary" -S "$socket" has-session -t '=work-two'
```

Save the complete program as `src/main/clojure/libtmux/examples/api/run_a_command.clj`, creating its parent directories. Closing its client leaves the launcher's server running.

[Source example](https://github.com/libtmux/libtmux-java/blob/5f88402151ff08fc0390dd438b90963692ec3fe4/examples/src/main/clojure/libtmux/examples/api/run_a_command.clj).

```clojure
(ns libtmux.examples.api.run-a-command
  "Use the preserved Java Pane ref to observe a command's real exit status."
  (:require [clojure.string :as str]
            [libtmux.core :as tm]
            [libtmux.data :as data])
  (:import [io.github.libtmux Pane PaneRun PaneRun$Outcome]
           [java.time Duration]))

(defn -main [& args]
  (when-not (= 3 (count args))
    (throw (IllegalArgumentException. "expected: tmux-binary socket-path config-file")))
  (let [[binary socket config] args]
    (with-open [server (tm/open! {:binary binary :socket-path socket :config-file config})]
      (let [session (tm/new-session! server {:name "command-example" :command ["/bin/sh"]})
            ^Pane pane (:tmux/ref (data/exactly-one (data/panes session)))
            ^PaneRun result (.run pane "printf 'built\\n'; exit 3" (Duration/ofMillis 900))]
        (assert (= PaneRun$Outcome/FINISHED (.outcome result)))
        (assert (= 3 (.orElseThrow (.exitStatus result))))
        (assert (= ["built"] (vec (.output result))))
        (println (str "exit=" (.orElseThrow (.exitStatus result))
                      " output=" (str/join " / " (.output result))))))))
```

Run it with the private fixture. Set TMUX_BIN to select another tmux binary:

```console
$ sh run.sh clojure \
  -J-Dclojure.main.report=stderr \
  -M \
  -m libtmux.examples.api.run-a-command
```

Expected output:

```text
exit=3 output=built
```

## Parameters

- `server`
- `options`

## tmux command

The tmux commands behind `new-session!`.

- [`new-session`](/en/tmux/latest/manual/new-session/)

## tmux C API

The C declarations in tmux that implement these commands.

- [`cmd_new_session_entry`](/en/tmux/latest/reference/c-variable-cmd_new_session_entry/) (attribute)
- [`cmd_new_session_exec`](/en/tmux/latest/reference/c-function-cmd-new-session-c-cmd_new_session_exec/) (function)

Each path starts at a function a command runs, which is degree 1. The degree counts steps from there along the path, and each step is a call or a reference: degree 2 is reached from that function, degree 3 from the next, and so on.

### Create a session and its first pane

1. [`cmd_new_session_exec`](/en/tmux/latest/reference/c-function-cmd-new-session-c-cmd_new_session_exec/) (function)
2. calls → [`spawn_window`](/en/tmux/latest/reference/c-function-spawn_window/) (function)
3. calls → [`spawn_pane`](/en/tmux/latest/reference/c-function-spawn_pane/) (function)
4. calls → [`window_add_pane`](/en/tmux/latest/reference/c-function-window_add_pane/) (function)
5. calls → [`window_pane_create`](/en/tmux/latest/reference/c-function-window-c-window_pane_create/) (function)

## Guides

Pages that discuss `new-session!`.

- [Captures, effects and streams](/en/clojure/latest/guides/captures-and-effects/)

## In other ports

Create a session

| Language | Equivalent |
| --- | --- |
| Python | [`libtmux.Server.new_session`](/en/py/latest/reference/libtmux-server-new_session/) (method) |
| Ruby | [`LibTmux::Server#new_session`](/en/ruby/latest/reference/libtmux-server-new_session/) (method) |
| Lua | [`libtmux.Server:new_session`](/en/lua/latest/reference/libtmux-server-new_session/) (method) |
| Erlang | [`tmux_session:create/2`](/en/erlang/latest/reference/tmux_session-create-2/) (function) |
| Haskell | No public Haskell equivalent is implemented; the current modules expose scalar values and version parsing. |
| TypeScript | [`server.Server.newSession`](/en/ts/latest/reference/server-server-newsession/) (method) |
| Rust | [`server.Server.new_session`](/en/rs/latest/reference/server-server-new_session/) (method) |
| Go | [`tmux.Server.NewSession`](/en/go/latest/reference/tmux-server-newsession/) (method) |
| Java | [`io.github.libtmux.Server.newSession`](/en/java/latest/reference/io-github-libtmux-server-server-newsession/) (method) |
| Kotlin | [`io.github.libtmux.kotlin.Server.newSession`](/en/kotlin/latest/reference/io-github-libtmux-kotlin-server-newsession/) (method) |
| Scala | [`io.github.libtmux.scaladsl.Server.newSession`](/en/scala/latest/reference/io-github-libtmux-scaladsl-server-newsession/) (method) |
| C# | [`LibTmux.Server.CreateSessionAsync`](/en/csharp/latest/reference/libtmux-server-createsessionasync/) (method) |
| C++ | [`libtmux::Server::new_session`](/en/cxx/latest/reference/libtmux-server-new_session/) (method) |
| Swift | [`Server.newSession(named:startDirectory:windowName:width:height:environment:shell:)`](/en/swift/latest/reference/server-newsession(named-startdirectory-windowname-width-height-)/) (method) |
| OCaml | [`Libtmux_unix.Client.create_session`](/en/ocaml/latest/reference/libtmux_unix-client-create_session/) (function) |
| Perl | [`LibTmux::Server::new_session`](/en/perl/latest/reference/libtmux-server-new_session/) (method). Explicit Server operation. Captured entities remain local observations; use a new snapshot to observe changes. |

No equivalent is recorded in PowerShell, Julia, Elixir, Common Lisp or F#.