modinfo: 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:

/sbin/modinfo - from package: module-init-tools

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

On Debian possible default full paths are:

/sbin/modinfo - from package: kmod

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

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