burp_ca: 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/sbin/burp_ca - from package: burp-client

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

On Debian possible default full paths are:

/usr/sbin/burp_ca - from package: burp

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

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