ctags: 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/ctags - from package: ctags

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

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