c_rehash: 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/c_rehash - from package: openssl-perl

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

On Debian possible default full paths are:

/usr/bin/c_rehash - from package: openssl

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

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