The number of processes created in Linux reaches 65535.

Creating processes on Linux is said to consume a small amount of time. This has always been a feature of Linux, so it specifically tests the limits of creating processes on Linux and tests the process.CodeAs follows:

 //  Fork. c  
 # Include <unistd. h>
# Include <stdlib. h>
# Include <stdio. h>
# Include < String . H>
 # Define # Maxprocess 65535
 # Define Sleeptime 60
 Int Main ( Int Argc, Char ** Argv ){
Pid_t PID;
 Int Count = 0 ;
 Int Maxprocess = maxprocess;
 If (Argc = 2 ){
Maxprocess = atoi (argv [ 1 ]);
}
 For (COUNT = 0 ; Count <maxprocess; count ++ ){
PID = fork ();
If (PID < 0 ){
Perror ( "  Fork Error  " );
Exit ( 1 );
} Else   If (Pid = 0 ){
Printf ( "  Child % d start \ n  " , Count );
Sleep (sleeptime );
Printf ( "  Child % d end \ n  " , Count );
Exit ( 0 );
}
Printf ( "  Parent: Create % d child \ n  " , Count );
}

 For (COUNT = 0 ; Count <maxprocess; count ++ ){
Wait ();
}
Exit ( 0 );

}

This code keeps creating sub-processes. By default, it creates 65535 processes. If the sub-processes cannot be created, an error is printed.

The test code is a blue account I created to run the test. To allow the process to create as many processes as possible, you must first set a hard limit on the number of processes created for the blue account.

Use the root account to modify the/etc/security/limits. conf file and add the following lines:

 
Blue hard nproc65535
 

Then, set the soft restrictions for the creation process for the blue account and execute the following code on the terminal:

 
Ulimit-u65535
 

At this point, although we set the hard and soft limits of the number of blue Account creation processes to 65535, we still cannot use the blue account to create 65535 processes, we also need to set Kernel Parameters in Linux. pid_max. this parameter is installed on 32768 by default. Therefore, even if the root account is used, this kernel parameter is not set. The maximum number of processes that can be created by the entire system is 32768, therefore, we need to make the following settings:

 
Sysctl-W kernel. pid_max =65535
 

Note: If the root account is used for executionProgramYou do not need to set hard and soft limits on resources, but you still need to set the Kernel Parameter of the maximum process PID value to create 65535 processes.

Switch to Blue account on the same terminal:

 
Su blue
 

Compile and execute the test code:

 
GCC fork. C-o fork
./Fork
 

My VM Linux memory is 512 MB. When I created more than processes, the program ran very slowly. Through the vmstat command, I found that swap memory was frequently placed, it can be determined that the virtual memory is insufficient, resulting in frequent Io operations, making the test code very slow. Therefore, when too many processes are created, the system memory is an important measure.

Later, I put the test code to a well-configured Xeon server for testing. The memory is 8 GB. When nearly processes are created, the program runs to a bottleneck and the memory bottleneck remains.

In the test code, the created sub-process occupies a relatively small amount of memory. In actual use, it may only use more memory than the process created in the test code, for machines with the same configuration, fewer available processes can be created.