montage: 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 CentOS possible default full paths are:

/usr/bin/montage - from package: ImageMagick

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/montage - from package: graphicsmagick-imagemagick-compat

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

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