i3-input: 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 Debian possible default full paths are:

/usr/lib/debug/usr/bin/i3-input - from package: i3-wm-dbg
/usr/bin/i3-input - from package: i3-wm

You may install the required package with command apt-get install {package}
Error in other languages:
i3-input: bevel nie gevind nie
i3-input: comandă negăsită
i3-input: comando não encontrado
i3-input: commande introuvable
i3-input: command not found
i3-input: käsku ei ole
i3-input: không tìm thấy lệnh
i3-input: komanda nerasta
i3-input: Kommando nicht gefunden.
i3-input: kommandot finns inte
i3-input: komut yok
i3-input: nie znaleziono polecenia
i3-input: níor aimsíodh an t-ordú
i3-input: no se encontró la orden
i3-input: no s'ha trobat l'ordre
i3-input: opdracht niet gevonden
i3-input: parancs nem található
i3-input: perintah tidak ditemukan
i3-input: príkaz nenájdený
i3-input: příkaz nenalezen
i3-input: команда не найдена
i3-input: командата не е открита
i3-input: 命令找不到
i3-input: コマンドが見つかりません