opendmarc: 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/opendmarc - from package: opendmarc

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

On Debian possible default full paths are:

/usr/sbin/opendmarc - from package: opendmarc

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

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