nginx: 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/sbin/nginx - from package: nginx16
/usr/sbin/nginx - from package: nginx18
/usr/sbin/nginx - from package: nginx

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

On Debian possible default full paths are:

/usr/sbin/nginx - from package: nginx-extras
/usr/sbin/nginx - from package: nginx-full
/usr/sbin/nginx - from package: nginx-light

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

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