equivs-control: command not found

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/bin/equivs-control - from package: equivs

You may install the required package with command apt-get install {package}

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