trial: 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/trial - from package: python-twisted-core

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

On Debian possible default full paths are:

/usr/bin/trial - from package: python-twisted-core

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

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