validate_mapping_file.py: 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/lib/qiime/bin/validate_mapping_file.py - from package: qiime

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

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