scanadf: 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 CentOS possible default full paths are:

/usr/bin/scanadf - from package: sane-frontends

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/scanadf - from package: sane

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

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