ykclient: 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/ykclient - from package: ykclient

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

On Debian possible default full paths are:

/usr/bin/ykclient - from package: libykclient-dev

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

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