mrinfo: 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 Debian possible default full paths are:

/usr/lib/mrtrix/bin/mrinfo - from package: mrtrix

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

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