groups: 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/groups - from package: coreutils

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

On Debian possible default full paths are:

/usr/bin/groups - from package: coreutils

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

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