varnishncsa: 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/varnishncsa - from package: varnish

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

On Debian possible default full paths are:

/usr/bin/varnishncsa - from package: varnish

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

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