vala-gen-introspect: 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/vala-gen-introspect - from package: vala-tools

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

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