gtkdoc-rebase: 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/gtkdoc-rebase - from package: gtk-doc

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

On Debian possible default full paths are:

/usr/bin/gtkdoc-rebase - from package: gtk-doc-tools

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

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