gctags: 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/gctags - from package: emacs-common

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

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