conmux: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/conmux - from package: conmux-client

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/conmux - from package: conmux

You may install the required package with command apt-get install {package}
Error in other languages:
conmux: bevel nie gevind nie
conmux: comandă negăsită
conmux: comando não encontrado
conmux: commande introuvable
conmux: command not found
conmux: käsku ei ole
conmux: không tìm thấy lệnh
conmux: komanda nerasta
conmux: Kommando nicht gefunden.
conmux: kommandot finns inte
conmux: komut yok
conmux: nie znaleziono polecenia
conmux: níor aimsíodh an t-ordú
conmux: no se encontró la orden
conmux: no s'ha trobat l'ordre
conmux: opdracht niet gevonden
conmux: parancs nem található
conmux: perintah tidak ditemukan
conmux: príkaz nenájdený
conmux: příkaz nenalezen
conmux: команда не найдена
conmux: командата не е открита
conmux: 命令找不到
conmux: コマンドが見つかりません