How do you mute from the command line?

Assuming you're using ALSA driver, run:

amixer set Master mute   
amixer set Master unmute

Or, you can just use:

amixer set Master toggle

to toggle mute on and off.

This worked for me when others didn't:

amixer -q -D pulse sset Master toggle

This is from the link in nutty about natty's comment to the first answer:

I'm using pactl in my scripts. From man page:

set-sink-mute SINK 1|0|toggle: Set the mute status of the specified sink (identified by its symbolic name or numerical index)

To mute:

pactl set-sink-mute @DEFAULT_SINK@ true

To unmute:

pactl set-sink-mute @DEFAULT_SINK@ false

To toggle:

pactl set-sink-mute @DEFAULT_SINK@ toggle

Use 0 instead of @DEFAULT_SINK@ to set the sink with numerical index 0. true=="1", false=="0".

Tested on Ubuntu 12.10.
In my setup sometimes amixer unmute fails for some reason.

On the terminal type this to mute

amixer set Master mute

type

amixer set Master unmute

Tested on my Ubuntu 10.10.

If you are using alsa follow goric answer.

PulseAudio is better, but not so simple: pactl set-sink-mute 0 1 Do the work for the first device, but not if you are using headphones of another sink output.

The better way is to check with pactl info and get the Default Sink to use.

DEFAULT_SINK=$(pactl info | grep "Default Sink" | cut -d " " -f3)

Then to mute:

pactl set-sink-mute "$DEFAULT_SINK" "1"

Or unmute:

pactl set-sink-mute "$DEFAULT_SINK" "0"

I wrote a script to manage pulseaudio in my note. If you want to use, save it as volume, provide execute permissions chmod +x volume and add it to your path ln -sv $PWD/volume /usr/local/bin/. Here my script:

#!/bin/bash
# script name: volume
# Author: glaudistong at gmail.com
# depends on: yad, coreutils, pulseaudio

ps -ef | grep "yad" | grep -E "Volume [^+\-]" | tr -s " " | cut -d " " -f2 | xargs -i kill "{}" 2>/dev/null
DEFAULT_SINK=$(pactl info | grep "Default Sink" | cut -d " " -f3)
DEFAULT_SOURCE=$(pactl info | grep "Default Source" | cut -d " " -f3)
case "$1" in 
    init)
    {
        ps -fe | grep yad | grep -q volume ||
        {
         yad --notification --command "volume up" --text "+ Volume +" --image ~/Pictures/volume-up-dark.png &
         yad --notification --command "volume down" --text "- Volume -" --image ~/Pictures/volume-down-dark.png &
        }
    };;
    up)
    {
        pactl set-sink-volume "$DEFAULT_SINK" +5%
        P=$(pactl list | grep -E "Name: $DEFAULT_SINK$|Volume" | grep "Name:" -A1 | tail -1 | cut -d% -f1 | cut -d/ -f2 | tr -d " ")
        iconl="$(echo -ne "\U1F50A")"
        iconr="$(echo -ne "\U1F56A")"
        timeout .6 yad --progress --percentage "$P" --timeout 1 --no-buttons --undecorated --text="$iconl Volume $P% $iconr" --no-focus --center --skip-taskbar --on-top &
    };;
    down)
    {
        pactl set-sink-volume "$DEFAULT_SINK" -5%
        P=$(pactl list | grep -E "Name: $DEFAULT_SINK$|Volume" | grep "Name:" -A1 | tail -1 | cut -d% -f1 | cut -d/ -f2 | tr -d " ")
        iconl="$(echo -ne "\U1F509")"
        iconr="$(echo -ne "\U1F569")"
        timeout .6 yad --progress --percentage "$P" --timeout 1 --no-buttons --undecorated --text="$iconl Volume $P% $iconr" --no-focus --center --skip-taskbar --on-top &
    };;
    mute)
    {
        ismute=$(pactl list | grep -E "Name: $DEFAULT_SINK$|Mute" | grep "Name:" -A1 | tail -1 |cut -d: -f2| tr -d " ")
        if [ "$ismute" == no ]; then
            s=1
            P=0
            icon="$(echo -ne "\U1F507")"
        else
            P=$(pactl list | grep -E "Name: $DEFAULT_SINK$|Volume" | grep "Name:" -A1 | tail -1 | cut -d% -f1 | cut -d/ -f2 | tr -d " ")
            icon="?"
            s=0
        fi
        pactl set-sink-mute "$DEFAULT_SINK" "$s"
        echo $s > /sys/devices/platform/thinkpad_acpi/leds/platform::mute/brightness
        timeout .6 yad --progress --percentage "$P" --timeout 1 --no-buttons --undecorated --text="$icon Volume $P%" --no-focus --center --skip-taskbar --on-top &
    };;
    mic-up)
    {
        pactl set-source-volume "$DEFAULT_SOURCE" +5%
        P=$(pactl list | grep -E "Name: $DEFAULT_SOURCE$|Volume" | grep "Name:" -A1 | tail -1 | cut -d% -f1 | cut -d/ -f2 | tr -d " ")
        icon="$(echo -en "\U1F3A4")"
        timeout .6 yad --progress --percentage "$P" --timeout 1 --no-buttons --undecorated --text="$icon Volume Mic $P%" --no-focus --center --skip-taskbar --on-top &
    };;
    mic-down)
    {
        pactl set-source-volume "$DEFAULT_SOURCE" -5%
        icon="$(echo -en "\U1F3A4")"
        P=$(pactl list | grep -E "Name: $DEFAULT_SOURCE$|Volume" | grep "Name:" -A1 | tail -1 | cut -d% -f1 | cut -d/ -f2 | tr -d " ")
        timeout .6 yad --progress --percentage "$P" --timeout 1 --no-buttons --undecorated --text="$icon Volume Mic $P%" --no-focus --center --skip-taskbar --on-top &
    };;
    mic-mute)
    {
        ismute=$(pactl list | grep -E "Name: $DEFAULT_SOURCE$|Mute" | grep "Name:" -A1 | tail -1 |cut -d: -f2| tr -d " ")
        if [ "$ismute" == no ]; then
            s=1
            P=0
            icon="$(echo -en "\U1F507\U1F3A4")"
        else
            P=$(pactl list | grep -E "Name: $DEFAULT_SOURCE$|Volume" | grep "Name:" -A1 | tail -1 | cut -d% -f1 | cut -d/ -f2 | tr -d " ")
            s=0
            icon="$(echo -en "\U1F3A4")"
        fi
        pactl set-source-mute "$DEFAULT_SOURCE" "$s"
        echo $s > /sys/devices/platform/thinkpad_acpi/leds/platform::micmute/brightness
        timeout .6 yad --progress --percentage "$P" --timeout 1 --no-buttons --undecorated --text="$icon Volume Mic $P%" --no-focus --center --skip-taskbar --on-top &
    };;
    *)
        echo invalid option;;
esac;

if your are using pulseaudio as the sound server then do this

pactl -- set-sink-mute @DEFAULT_SINK@ toggle # Also true/false to mute/unmute

to mute and unmute

if using alsa then use this

amixer sset 'Master' toggle

to mute and unmute