sethost: 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/sethost - from package: dnet-progs

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

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