formatdb: 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/formatdb - from package: blast2
/usr/share/ncbi-blast+/bin/formatdb - from package: ncbi-blast+-legacy

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

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