SocketServer: 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/SocketServer - from package: vtk-testing

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

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