R: 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/R - from package: R-core
/usr/lib64/R/bin/exec/R - from package: R-core
/usr/lib64/R/bin/R - from package: R-core
/usr/lib/R/bin/exec/R - from package: R-core
/usr/lib/R/bin/R - from package: R-core
/usr/bin/R - from package: R-littler

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

On Debian possible default full paths are:

/usr/bin/R - from package: littler
/usr/bin/R - from package: r-base-core
/usr/lib/R/bin/exec/R - from package: r-base-core
/usr/lib/R/bin/R - from package: r-base-core
/usr/lib/debug/usr/lib/R/bin/exec/R - from package: r-base-core-dbg

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

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