sdeconv: 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/lib/mrtrix/bin/sdeconv - from package: mrtrix

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

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