sff-dump: 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/sff-dump - from package: sra-toolkit

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

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