opensipsunix: 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/opensipsunix - from package: opensips

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

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