varnishstat: 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/varnishstat - from package: varnish

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

On Debian possible default full paths are:

/usr/bin/varnishstat - from package: varnish

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

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