link: 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:

/bin/link - from package: coreutils
/usr/lib/golang/pkg/bootstrap/bin/link - from package: golang-bin
/usr/lib64/R/bin/LINK - from package: R-core
/usr/lib/R/bin/LINK - from package: R-core

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

On Debian possible default full paths are:

/usr/lib/R/bin/LINK - from package: r-base-core
/usr/bin/link - from package: coreutils

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

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