texdef: 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/bin/texdef - from package: texlive-extra-utils

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

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