merge_mapping_files.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/merge_mapping_files.py - from package: qiime

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

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