unixgroup: 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/unixgroup - from package: pwauth

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

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