varnishhist: 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/varnishhist - from package: varnish

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

On Debian possible default full paths are:

/usr/bin/varnishhist - from package: varnish

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

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