varnishadm: 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/varnishadm - from package: varnish

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

On Debian possible default full paths are:

/usr/bin/varnishadm - from package: varnish

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

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