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In my dmesg this appeared when my window manager (xfwm4, part of XFCE) crashed:

xfwm4[3936]: segfault at 7f3c7c523770 ip 00007f3c7c523770 sp 00007ffffea1ee28 error 15 in SYSV00000000 (deleted)[7f3c7c4e8000+60000]

The same SYSV00000000 also appears in other places (like lsof). So, what is this SYSV00000000? I Googled around and found that it's related to virtual memory, but not much else.

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up vote 8 down vote accepted

The kernel is telling you that when the segfault occurred, the instruction pointer 0x7f3c7c523770 was in a SysV IPC shm segment. The shared memory segment started at 0x7f3c7c4e8000 and was 0x60000 bytes long.

SysV shm segments are not backed by a file, so the string SYSV00000000 appears where normally you'd get the filename of the executable or library where the segfault occurred. As a result this log line gives us no real useful information. If you want any hope of tracing the cause of the crash, you need the core dump.

I suspect that the instruction pointer wasn't supposed to be in there at all. It's pretty weird to load executable code into a SysV shm segment. But I haven't seen any XFCE code, so what looks weird to me might be normal there.

You can learn the basics about sysv shm, assuming you have a decent grasp of the basics of memory management by reading these man pages:

man svipc
man shmget
man shmat

Run the ipcs command to see what sysv ipc resources are currently allocated. ipcs -m limits the list to just the shared memory segments.

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