fastaq_interleave: 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/fastaq_interleave - from package: fastaq

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

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