squid: 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/sbin/squid - from package: squid34
/usr/sbin/squid - from package: squid

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

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