ykpamcfg: 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/ykpamcfg - from package: pam_yubico

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

On Debian possible default full paths are:

/usr/bin/ykpamcfg - from package: libpam-yubico

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

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