varnishtop: 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/varnishtop - from package: varnish

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

On Debian possible default full paths are:

/usr/bin/varnishtop - from package: varnish

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

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