The Unix time was born January First 1970 exactly at 12 AM with no minutes and seconds. Its age already exceeds 1 billion and 600 millions seconds or 0x5F5E1000 in hex value, so far it is good for 32-bit positive signed integer, but until Tuesday, January 19, 2038 when this number becomes 32-bit negative integer. The year 2038 problem is sometimes referred to as the Y2K38 problem. Switching to 64-bit integer will significantly extend life of Unix time because maximum value of time_t (64 bit signed integer) is 0x7FFFFFFFFFFFFFFF.
Look at the Unix time heartbeats:
Now let us test how some Linux systems are vulnerable to Y2K38 problem, using this simple code to test what happens after time_t reaches 0x7ffffff value:
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#include <stdio.h> #include <time.h> int main(int, char **) { char szBuffer[64]; printf("Size of time_t: %d bits\n", 8*sizeof(time_t)); time_t currentTime = time(NULL); struct tm * timeinfo = gmtime( ¤tTime ); printf("Unix: 0x%x value. Current UTC time: %s\n", (unsigned int)currentTime, asctime(timeinfo)); unsigned int y38Time = 0x7fffffff; for(unsigned int iTime = y38Time-5; iTime < y38Time+5; iTime++) { time_t tTime = (const time_t)iTime; timeinfo = gmtime( &tTime ); printf("Unix: 0x%x value. UTC time: %s", iTime, asctime(timeinfo)); } return 0; } |
Test it on Ubuntu 14.04 32-bit:
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8# ./y38 Size of time_t: 32 bits Unix: 0x5fd21d1c value. Current UTC time: Thu Dec 10 13:05:32 2020 Unix: 0x7ffffffa value. UTC time: Tue Jan 19 03:14:02 2038 |
The size of time_t (signed integer) is 32 bit. On 03:14:07 19 January 2038 time_t will be equal to 0x7fffffff and 1 second after will become negative and system will interpret it as 20:45:52 on Friday, 13 December 1901 rather than 03:14:08 19 January 2038. So without proper upgrade the timing of this 32 bit OS will stop working as expected.
Now what happens on CentOS 8 64 bit.
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# ./y38 Size of time_t: 64 bits Unix: 0x5fd18046 value. Current UTC time: Thu Dec 10 01:56:22 2020 Unix: 0x7ffffffa value. UTC time: Tue Jan 19 03:14:02 2038 |
The size of time_t (signed integer) is 64 bit and there is no Y2K38 problem in this 64 bit OS and I expect that other 64 bit systems will be OK after Jan 19 2038 as well.
The question is how many 32 bit systems will be in use it 2038?