svnadmin: 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/svnadmin - from package: subversion

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

On Debian possible default full paths are:

/usr/bin/svnadmin - from package: subversion

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

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