By default, on Ubuntu, a process can only attach to another process if it has a predefined relationship with it. An example would be a parent process that has started a child process. This is a restriction to ptrace and is valid for non-root users only. It is designed to ensure higher security to malware attacks. The root user can still attach to any process.
This affects unsolicited Dynamic Attachment debugging.
This behavior is defined by the sysctl value in /proc/sys/kernel/yama/ptrace_scope, which is set to 1, by default.
To relax the restriction and allow processes to attach to other processes, this value must be set to 0. This allows processes that have the same user id to attach to each other. Execute the following to remove the restriction:
sudo sh << END echo 0 > /proc/sys/kernel/yama/ptrace_scope END
The following table shows which debugging methods need you to do this:
| Debugging method | sysctl value in ptrace_scope |
|---|---|
| Local debugging using Eclipse | Either 0 or 1 |
| Debugging using local attach to process with Eclipse (attach to PID) | Must be 0 |
| anim <prog> | Either 0 or 1 |
| COBSW=+A <prog> | Either 0 or 1 |
| anim <pid> | Must be 0 |
| cobanimsrv | Either 0 or 1 |
| CBL_DEBUG_START | Either 0 or 1 |
| debug_on_error tunable | Either 0 or 1 |
| core_on_error tunable | Either 0 or 1 |
| stackdump_on_error tunable | Either 0 or 1 |
| Remote debugging using Eclipse | Either 0 or 1 |
| Debugging using remote attach to process with Eclipse (attach to PID) | Must be 0 |
For more on the ptrace restriction, check the Ubuntu documentation.