tkcvs: 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/tkcvs - from package: tkcvs

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

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