Can't connect to Internet in bash using Mac OS

Question

My browser works perfectly using the using Internet, however, when I tried to use this command in bash:

ping -q -w1 -c1 google.com &>/dev/null && echo online || echo offline

It gives me "offline" results. I have also tried another one in a different network:

ping -c 3 www.google.com

It returns:

PING www.google.com (74.125.193.147): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1

--- www.google.com ping statistics ---
3 packets transmitted, 0 packets received, 100.0% packet loss

All of these seem to point out that the terminal couldn't reach to the internet. I have tried using wifi and lan cable, the outcomes are the same.

I need to run a program which requires connection to a server, I wonder if you have any solutions to switch it back to online. I'm on macOS 10.13 and am looking to determine from the command line if a network connection is viable.

Is this possible?

Answer 1

I prefer to use the system configuration utility tool to test for reachability instead of using ping / host / nslookup or another proxy for determining if a network entity is or is not reachable.

scutil -r google.com
Reachable

The benefits of this are that if you have VPN connections, dial up, modem, or a routing conflict, this will actually test that you can reach the device and not just resolve the cached host name, etc... in my experience. (also, it's a lot harder to mess up the indirection, files, logic and you get a direct answer back in English)

Like all good command line tools, it returns 0 to let you know the answer it provides is confident and an error if you have problems testing reachability.

 -r [-W] { nodename | address | local-address remote-address }
     Check the network reachability of the specified host name, IP
     address, or a pair of local and remote IP addresses.  One or more of
     the following strings will be reported to standard output.

     Not Reachable         The specified nodename/address cannot be
                           reached using the current network configura-
                           tion.

     Reachable             The specified nodename/address can be reached
                           using the current network configuration.

     Transient Connection  The specified nodename/address can be reached
                           via a transient (e.g. PPP) connection.

     Connection Required   The specified nodename/address can be reached
                           using the current network configuration but a
                           connection must first be established.  As an
                           example, this status would be returned for a
                           dialup connection that was not currently active
                           but could handle network traffic for the target
                           system.

     Connection Automatic  The specified nodename/address can be reached
                           using the current network configuration but a
                           connection must first be established.  Any
                           traffic directed to the specified name/address
                           will initiate the connection.

     Local Address         The specified nodename/address is one associ-
                           ated with a network interface on the system.

     Directly Reachable Addresss
                           Network traffic to the specified node-
                           name/address will not go through a gateway but
                           is routed directly to one of the interfaces on
                           the system.

     The reachability can also be monitored by specifying the -W (watch)
     option.  This will result in the current status being reported as
     well as the status when/if the network configuration changes.

     A zero exit status will be returned when the reachability status is
     reported correctly.  A non-zero exit status will be returned if
     errors are detected with an error reported to standard error.

Since Apple's index of manual pages is a PITA to use, here's a hopefully more stable link to the entire manual page online: https://ss64.com/osx/scutil.html

As a bonus - here is another decent Q&A relating to scutil and checking resolution: nslookup & dig fail; ping, traceroute, and scutil -r work

Answer 2

Your problem is that you're using invalid options for the ping command. It seems likely that you have copied a command line intended for use on Linux, and tried to use it unmodified on macOS.

The specific problem here is that Linux uses "-w" to specify timeouts, whereas macOS uses "-t". This means that your command line should instead be this:

ping -q -t1 -c1 google.com &>/dev/null && echo online || echo offline

Answer 3

Your command ping -c 3 www.google.com should have produced 3 internet response packets of the type ICMP ECHO REPLY. The ping command sends ECHO packets using the ICMP protocol, and the responses (if any) are ECHO REPLY packets. The curl command on the other hand, sends HTTP packets using the TCP protocol. Since the latter works and the former doesn't, there is probably something between your machine and www.google.com that blocks the ICMP protocol. A lot of misconfigured firewalls do this, so that is where I would start looking for the cause.

Blocking ICMP is bad practice since it stops things like Path MTU Discovery from working (MTU = Maximum Transmission Unit size). This stops most traffic from working if the remote MTU is smaller than the local MTU. So it's an extremely bad idea to block ICMP in the firewall.