khost: 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/khost - from package: knot

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

On Debian possible default full paths are:

/usr/bin/khost - from package: knot-host

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

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