ykksm-import: 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/ykksm-import - from package: yubikey-ksm

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

On Debian possible default full paths are:

/usr/bin/ykksm-import - from package: yubikey-ksm

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

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