> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/tmux/tmux/llms.txt
> Use this file to discover all available pages before exploring further.

# Terminal Features

> Terminal feature detection and capability management in tmux

## Overview

tmux includes a sophisticated terminal feature detection system that automatically identifies and enables advanced terminal capabilities. This allows tmux to provide enhanced functionality when the underlying terminal supports it.

## Terminal Features System

### Feature Detection

tmux detects terminal features through multiple mechanisms:

* **terminfo capabilities**: Standard terminal database entries
* **Terminal type identification**: Recognizing specific terminal emulators
* **Device Attributes (DA)**: Querying the terminal at runtime
* **Manual specification**: Using the `terminal-features` option

The feature detection code is implemented in `tty-features.c`.

### Available Terminal Features

tmux supports the following terminal features:

#### Color Support

<CodeGroup>
  ```bash 256 Colors theme={null}
  # Enable 256 color support
  set -g terminal-features "xterm*:256"
  ```

  ```bash RGB/True Color theme={null}
  # Enable 24-bit RGB color support
  set -g terminal-features "xterm*:RGB"
  ```
</CodeGroup>

From `tty-features.c:116-128`, the RGB feature includes:

* `setrgbf`: Set RGB foreground color (\E\[38;2;%p1%d;%p2%d;%p3%dm)
* `setrgbb`: Set RGB background color (\E\[48;2;%p1%d;%p2%d;%p3%dm)
* Support for 256-color palette alongside RGB

#### Text Attributes

<AccordionGroup>
  <Accordion title="Strikethrough" icon="strikethrough">
    Enables strikethrough text formatting:

    ```bash theme={null}
    set -g terminal-features "*:strikethrough"
    ```

    Implemented as escape sequence: `\E[9m`
  </Accordion>

  <Accordion title="Overline" icon="overline">
    Enables overline text attribute:

    ```bash theme={null}
    set -g terminal-features "*:overline"
    ```

    Sequence: `Smol=\E[53m` (from `tty-features.c:144-152`)
  </Accordion>

  <Accordion title="Underscore Styles" icon="underline">
    Advanced underscore styling with colors:

    ```bash theme={null}
    set -g terminal-features "*:usstyle"
    ```

    Supports:

    * Different underscore types (single, double, curly, dotted, dashed)
    * Underscore colors independent of text color
    * RGB colors for underscores

    From `tty-features.c:155-166`:

    * `Smulx`: Set underscore style
    * `Setulc`: Set underscore RGB color
    * `Setulc1`: Set underscore palette color
  </Accordion>
</AccordionGroup>

#### Advanced Features

<CardGroup cols={2}>
  <Card title="Title Setting" icon="window">
    Window title escape sequences:

    ```bash theme={null}
    set -g terminal-features "*:title"
    ```

    From `tty-features.c:51-60`:

    * `tsl=\E]0;` - To status line
    * `fsl=\a` - From status line
  </Card>

  <Card title="Clipboard" icon="clipboard">
    OSC 52 clipboard integration:

    ```bash theme={null}
    set -g terminal-features "*:clipboard"
    ```

    Sequence: `Ms=\E]52;%p1%s;%p2%s\a` (`tty-features.c:86-94`)
  </Card>

  <Card title="Mouse Support" icon="mouse-pointer">
    Xterm-style mouse tracking:

    ```bash theme={null}
    set -g terminal-features "*:mouse"
    ```

    Capability: `kmous=\E[M` (`tty-features.c:75-83`)
  </Card>

  <Card title="Focus Reporting" icon="eye">
    Focus in/out events:

    ```bash theme={null}
    set -g terminal-features "*:focus"
    ```

    From `tty-features.c:181-190`:

    * Enable: `Enfcs=\E[?1004h`
    * Disable: `Dsfcs=\E[?1004l`
  </Card>
</CardGroup>

#### Cursor Customization

```bash Cursor Styles theme={null}
# Enable cursor style changes
set -g terminal-features "*:cstyle"
```

From `tty-features.c:193-202`:

* `Ss=\E[%p1%d q` - Set cursor style
* `Se=\E[2 q` - Reset cursor style

Supports various cursor shapes: block, underline, bar, with blinking variants.

```bash Cursor Colors theme={null}
# Enable cursor color customization
set -g terminal-features "*:ccolour"
```

From `tty-features.c:205-214`:

* `Cs=\E]12;%p1%s\a` - Set cursor color
* `Cr=\E]112\a` - Reset cursor color

#### Modern Terminal Features

<Tabs>
  <Tab title="Extended Keys">
    Enhanced keyboard protocol support:

    ```bash theme={null}
    set -g terminal-features "*:extkeys"
    ```

    From `tty-features.c:239-248`:

    * Enable: `Eneks=\E[>4;2m`
    * Disable: `Dseks=\E[>4m`

    Allows distinguishing more key combinations.
  </Tab>

  <Tab title="Synchronized Updates">
    Reduces flickering during redraws:

    ```bash theme={null}
    set -g terminal-features "*:sync"
    ```

    Sequence: `Sync=\E[?2026%?%p1%{1}%-%tl%eh%;` (`tty-features.c:228-236`)
  </Tab>

  <Tab title="Hyperlinks">
    OSC 8 hyperlink support:

    ```bash theme={null}
    set -g terminal-features "*:hyperlinks"
    ```

    From `tty-features.c:97-109`:

    * `Hls=\E]8;%?%p1%l%tid=%p1%s%;;%p2%s\E\\`
  </Tab>

  <Tab title="Bracketed Paste">
    Safe paste mode detection:

    ```bash theme={null}
    set -g terminal-features "*:bpaste"
    ```

    From `tty-features.c:169-178`:

    * Enable: `Enbp=\E[?2004h`
    * Disable: `Dsbp=\E[?2004l`
  </Tab>
</Tabs>

#### Graphics Features

<Warning>
  Graphics features require terminal support and compile-time configuration.
</Warning>

```bash Sixel Graphics theme={null}
set -g terminal-features "*:sixel"
```

From `tty-features.c:350-358`, enables sixel image support when compiled with the appropriate libraries.

```bash DECFRA Rectangle Fill theme={null}
set -g terminal-features "*:rectfill"
```

From `tty-features.c:265-273`, enables fast rectangle filling operations:

* Capability: `Rect`
* Used for optimized screen redraws

```bash DECSLRM Margins theme={null}
set -g terminal-features "*:margins"
```

From `tty-features.c:251-262`, scroll region margins:

* Enable: `Enmg=\E[?69h`
* Disable: `Dsmg=\E[?69l`
* Set margins: `Cmg=\E[%i%p1%d;%p2%ds`

## Default Terminal Configurations

tmux includes predefined feature sets for popular terminals (from `tty-features.c:468-514`):

### Modern Terminals Base Set

Most modern terminals support:

```
256,RGB,bpaste,clipboard,mouse,strikethrough,title
```

<Tabs>
  <Tab title="tmux">
    When running tmux inside tmux:

    ```
    256,RGB,bpaste,clipboard,mouse,strikethrough,title,
    ccolour,cstyle,focus,overline,usstyle,hyperlinks
    ```
  </Tab>

  <Tab title="iTerm2">
    ```
    256,RGB,bpaste,clipboard,mouse,strikethrough,title,
    cstyle,extkeys,margins,usstyle,sync,osc7,hyperlinks
    ```
  </Tab>

  <Tab title="XTerm">
    ```
    256,RGB,bpaste,clipboard,mouse,strikethrough,title,
    ccolour,cstyle,extkeys,focus
    ```

    Note: XTerm also supports margins and rectfill, but they can be disabled, so tmux detects them via secondary DA.
  </Tab>

  <Tab title="mintty">
    ```
    256,RGB,bpaste,clipboard,mouse,strikethrough,title,
    ccolour,cstyle,extkeys,margins,overline,usstyle
    ```
  </Tab>

  <Tab title="foot">
    ```
    256,RGB,bpaste,clipboard,mouse,strikethrough,title,
    cstyle,extkeys
    ```
  </Tab>

  <Tab title="rxvt-unicode">
    ```
    256,bpaste,ccolour,cstyle,mouse,title,ignorefkeys
    ```

    Note: rxvt-unicode has quirky function key handling, so tmux uses `ignorefkeys` to use built-in sequences instead.
  </Tab>
</Tabs>

## Configuration Examples

### Override Terminal Type

Force specific features for all terminals:

```bash ~/.tmux.conf theme={null}
# Enable all supported features for any xterm-compatible terminal
set -g terminal-features "xterm*:256:RGB:cstyle:ccolour:clipboard:title:mouse:focus"

# Enable features for tmux terminals specifically
set -ga terminal-features "tmux*:hyperlinks:sync:usstyle:overline"

# Enable strikethrough for all terminals
set -ga terminal-features "*:strikethrough"
```

### Working Directory Tracking

```bash OSC 7 Support theme={null}
# Enable working directory tracking
set -g terminal-features "*:osc7"

# Capability from tty-features.c:63-72:
# Swd=\E]7; fsl=\a
```

### Disable Specific Features

To disable features that cause problems:

```bash theme={null}
# Don't use terminal's function keys (use tmux built-ins)
set -g terminal-features "rxvt*:ignorefkeys"
```

From `tty-features.c:276-347`, this disables `kf0` through `kf63` terminal capabilities.

## Feature Application

<Steps>
  <Step title="Feature Detection">
    tmux applies features in this order:

    1. Default features based on `$TERM` environment variable
    2. Device Attributes response (if available)
    3. User-specified `terminal-features` option
  </Step>

  <Step title="Capability Override">
    From `tty-features.c:434-464`, when features are applied:

    ```c theme={null}
    for (i = 0; i < nitems(tty_features); i++) {
        if ((term->features & (1 << i)) || (~feat & (1 << i)))
            continue;
        tf = tty_features[i];
        
        log_debug("applying terminal feature: %s", tf->name);
        if (tf->capabilities != NULL) {
            capability = tf->capabilities;
            while (*capability != NULL) {
                log_debug("adding capability: %s", *capability);
                tty_term_apply(term, *capability, 1);
                capability++;
            }
        }
        term->flags |= tf->flags;
    }
    ```
  </Step>

  <Step title="Verification">
    Check active features:

    ```bash theme={null}
    # From outside tmux
    tmux show -g terminal-features

    # Check detected features in server info
    tmux info | grep features
    ```
  </Step>
</Steps>

## Best Practices

<Check>
  Let tmux auto-detect features when possible - manual overrides may cause issues
</Check>

<Check>
  Test feature changes thoroughly - some terminals report capabilities they don't fully support
</Check>

<Check>
  Use wildcards carefully - `*` matches all terminal types
</Check>

<Warning>
  Some features interact with terminal settings. For example:

  * `extkeys` requires terminal support for the extended keyboard protocol
  * `sync` may cause artifacts on slow connections
  * `margins` can conflict with certain terminal scrollback implementations
</Warning>

## Debugging Features

Enable tmux logging to see feature detection:

```bash theme={null}
# Start tmux with verbose logging
tmux -vvv new-session

# Check tmux-client-*.log for lines like:
# "adding terminal feature: RGB"
# "adding capability: setrgbf=..."
```

## Related Configuration

* [`terminal-overrides`](/options/global#terminal-overrides) - Override specific capabilities
* [`default-terminal`](/options/global#default-terminal) - Set TERM value inside tmux
* [`allow-passthrough`](/options/global#allow-passthrough) - Control escape sequence passthrough