ypcat: 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/ypcat - from package: yp-tools

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

On Debian possible default full paths are:

/usr/bin/ypcat - from package: nis

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

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