tex2lyx: 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/tex2lyx - from package: lyx

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

On Debian possible default full paths are:

/usr/bin/tex2lyx - from package: lyx

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

Error in other languages:
tex2lyx: bevel nie gevind nie
tex2lyx: comandă negăsită
tex2lyx: comando não encontrado
tex2lyx: commande introuvable
tex2lyx: command not found
tex2lyx: käsku ei ole
tex2lyx: không tìm thấy lệnh
tex2lyx: komanda nerasta
tex2lyx: Kommando nicht gefunden.
tex2lyx: kommandot finns inte
tex2lyx: komut yok
tex2lyx: nie znaleziono polecenia
tex2lyx: níor aimsíodh an t-ordú
tex2lyx: no se encontró la orden
tex2lyx: no s'ha trobat l'ordre
tex2lyx: opdracht niet gevonden
tex2lyx: parancs nem található
tex2lyx: perintah tidak ditemukan
tex2lyx: príkaz nenájdený
tex2lyx: příkaz nenalezen
tex2lyx: команда не найдена
tex2lyx: командата не е открита
tex2lyx: 命令找不到
tex2lyx: コマンドが見つかりません