lyxclient: 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/lyxclient - from package: lyx

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

On Debian possible default full paths are:

/usr/bin/lyxclient - from package: lyx

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

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