mongos: 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/mongos - from package: mongodb-server

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

On Debian possible default full paths are:

/usr/bin/mongos - from package: mongodb-server

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

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