fab: 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/fab - from package: fabric

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

On Debian possible default full paths are:

/usr/bin/fab - from package: fabric

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

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