fasttree: 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/fasttree - from package: fasttree
/usr/lib/qiime/bin/FastTree - from package: qiime

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

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