tred: 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/tred - from package: graphviz

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

On Debian possible default full paths are:

/usr/bin/tred - from package: graphviz

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

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