blast2: 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/blast2 - from package: blast2

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

Error in other languages:
blast2: bevel nie gevind nie
blast2: comandă negăsită
blast2: comando não encontrado
blast2: commande introuvable
blast2: command not found
blast2: käsku ei ole
blast2: không tìm thấy lệnh
blast2: komanda nerasta
blast2: Kommando nicht gefunden.
blast2: kommandot finns inte
blast2: komut yok
blast2: nie znaleziono polecenia
blast2: níor aimsíodh an t-ordú
blast2: no se encontró la orden
blast2: no s'ha trobat l'ordre
blast2: opdracht niet gevonden
blast2: parancs nem található
blast2: perintah tidak ditemukan
blast2: príkaz nenájdený
blast2: příkaz nenalezen
blast2: команда не найдена
blast2: командата не е открита
blast2: 命令找不到
blast2: コマンドが見つかりません