circo: 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/circo - from package: graphviz

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

On Debian possible default full paths are:

/usr/bin/circo - from package: graphviz

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

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