salt-key: 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 CentOS possible default full paths are:

/usr/bin/salt-key - from package: salt-master

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

On Debian possible default full paths are:

/usr/bin/salt-key - from package: salt-master

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

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