spatialite_convert: 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/spatialite_convert - from package: spatialite-bin

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

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