Problem
At Mid-Autumn Festival this year, I took out my iBook G4 which os is Mac OS X 10.5.8 wanting to change its package manager from homebrew to macports. But it starts stalling only after connected to the Internet. Why it happened?
Investigation
First I have found that when the system starts stalling, current window is still respoding, while the cursor turns to circling moving on other windows. This phenomenon is very likely to disk IO not responding.
About a year before, my Mac Mini(Late 2014) showed the same phenomenon because I had installed a third-party SATA SSD without manually turning on TRIM. At that time I replaced the SSD then manually turned on TRIM. The Mac Mini returned to normal since then.
I thought that the SSD (MSATA converted to PATA 2.5-inch) installed on the iBook G4 without TRIM resulted in this problem. So I have purchased another SSD, then replaced the first one. To my suprised, the new SSD shows the same stalling. And I testd the first SSD, it performs well.
It seems that the stalling is not related to disk IO. I have searched this problem, but there is no valid solution. I have changed the AP, and tested wired connection, the stalling certainly comes after a while.
When I nearly gave up, the dawn starts shining. I have connected to my secondary ISP gateway WIFI, the stalling disappeared. I found that this ISP is not providing IPv6 addresses. If it is the true reason of stalling?
Solution
I turned off IPv6 at Network Panel in System Preferences, then switched the WIFI to ISP which providing IPv6. This time the system works so well. Maybe Mac OS X 10.5.8 has some bug on IPv6 network stack. Finally I could operate my iBook G4 normally~