fastq_to_fasta: 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/fastq_to_fasta - from package: fastx-toolkit

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

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