sethead: 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/sethead - from package: wcstools

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

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