ansible: 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/ansible - from package: ansible

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

On Debian possible default full paths are:

/usr/bin/ansible - from package: ansible

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

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