preline: 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/preline - from package: qmail
/var/lib/qmail/bin/preline - from package: qmail

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

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