gpg: 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/gpg - from package: gnupg2

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

On Debian possible default full paths are:

/usr/bin/gpg - from package: gnupg

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

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