ykgenerate: 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/ykgenerate - from package: libyubikey

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

On Debian possible default full paths are:

/usr/bin/ykgenerate - from package: libyubikey-dev

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

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