mongodump: 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/mongodump - from package: mongodb

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

On Debian possible default full paths are:

/usr/bin/mongodump - from package: mongodb-clients

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

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