What to do if Linux does not generate core files

Solutions for Linux not generating core files: 1. Check whether the Core dump directory exists and set the process to have write permissions for the directory; 2. Check whether the service program calls seteuid(); 3. Set it to be large enough Core file size limit; 4. Modify profile, etc.

#The operating environment of this article: linux5.9.8 system, Dell G3 computer.

What should I do if Linux does not generate core files? Why is the core file not generated?

1. Make sure that the directory where the Core dump is stored exists and that the process has write permissions to the directory.

The directory where the Core dump is stored is the current directory of the process, which is generally the directory where the process was located when the command was issued to start the process. But if it is started through a script, the script may modify the current directory. In this case, the real current directory of the process will be different from the directory where the script was originally executed. At this time, you can view the target of the "/proc//cwd" symbolic link to determine the real current directory address of the process. Processes started through system services can also be viewed through this method.

2. If the program calls seteuid()/setegid() to change the effective user or group of the process, the system will not generate Core dump for these processes by default.

Many service programs will call seteuid(), such as MySQL. No matter what user you use to run mysqld_safe to start MySQL, the effective user for mysqld is always the msyql user. If you originally ran a program as user A, but the user of the program you see in PS is B, then these processes have called seteuid. In order to enable these processes to generate Coredump, (echo "1" > /proc/sys/kernel/suid_dumpable) is required.

3. As we all know, we need to set a large enough Core file size limit.

The size of the Core file generated when the program crashes is the size of the memory occupied by the program when it is running. However, the behavior when the program crashes cannot be estimated based on the normal behavior. For example, errors such as buffer overflow may cause the stack to be destroyed. Therefore, the value of a certain variable is often modified into a mess, and then the program uses this size to apply for memory. This may cause the program to occupy a lot more memory than usual. Therefore, no matter how little memory the program occupies during normal operation, it is better to ensure that the Core file is generated and the size limit is set to unlimited.

4. Add:

ulimit -c unlimited > /dev/null 2?&1

to /etc/profile 5. Programs that are generally started on the CLI can be terminated outside the program if you set:

ulimit -c unlimited

Generate core dump file. However, for programs running in daemon mode, the main difference from programs started by CLI is the running environment of the process, which includes

cwd (current working directory). If you define the format of the core file using a relative path, for example, define /proc/sys/kernel/core_pattern as:

core-%e-%p-%t

Generally speaking, the cwd of the daemon file is /, and you can pass /proc/< your_program_pid>/cwd to view, usually connect to the / directory. And if the user does not have write permissions for this directory, then the core dump file will not be generated.

The most direct solution is to modify /proc/sys/kernel/core_pattern to the absolute path: /data/coredump/core-%e-%p-%t

and ensure This is basically OK.

Modify the core dump file format in the /proc/sys/kernel/core_pattern file to an absolute path, for example:

/data/coredump/core-%e-%p-%t

When will the core file not be generated?

The core file will not be generated under the following conditions:

(a) The process is set-user-ID, and the current user is not the owner of the program file;

(b) The process is set-group-ID, and the current user is not the group owner of the program file;

(c) The user does not have permission to write to the current working directory;

( d) The file is too large. The permissions of the core file (assuming the file did not exist before this) are usually user read/write, group read and other read.

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