varnishd: 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/sbin/varnishd - from package: varnish

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

On Debian possible default full paths are:

/usr/sbin/varnishd - from package: varnish

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

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