3 ms·

This was actually a problem on dash, so I added several more signals (INT TERM etc.). Nothing saves you from kill -9, as we all know. I did add a reboot entry

by chasil 4y ago

This was actually a problem on dash, so I added several more signals (INT TERM etc.). Nothing saves you from kill -9, as we all know. I did add a reboot entry to cron (@reboot with Vixie cron) to remove the directory. I can say that this method has processed millions of Oracle archived logs with no errors.

bombcar 4y ago
I wonder if the fact that you can delete a file and still access its contents as long as a file descriptor is still open would allow some dorty magic. Probably not because iirc you can create a file with the same name right after deletion even if a fd is open to the old one.
- chasil 4y ago
  SQLite will open temporary files (for sorting and sundry functions), then immediately unlink() them. This is allowed behavior under POSIX. The NFS trick was documented in "Why NFS Sucks" by Olaf Kirch. "Some other cases are a bit stranger. One such case is the ability to write to an open unlinked file. POSIX says an application can open a file for reading and writing, unlink it, and continue to do I/O on it. The file is not supposed to go away until the last application closes it. "This is difficult to do over NFS, since traditionally, the NFS server has no concept of “open” files (this was added in NFSv4, however). So when a client removes a file, it will be gone for good, and the file handle is no longer valid— and attempt to read from or write to that file will result in a “Stale file handle” error. "The way NFS traditionally kludges around this is by doing what has been dubbed a “silly re- name.” When the NFS client notices during an unlink call that one or more applications still hold an open file descriptor to this file, it will not send a REMOVE call to the server. Instead, it will rename the file to some temporary file name, usually .nfsXXX where XXX is some hex number. This file will stay around until the last application closes its open file descriptor, and only then will the NFS client send the final REMOVE call to the server that gets rid of this renamed file. "This sounds like a rather smart sleight of hand, and it is—up to a point. First off, this does not work across different clients. But that should not come as a surprise given the lack of cache consistency." https://www.kernel.org/doc/ols/2006/ols2006v2-pages-59-72.pdf https://www.kernel.org/doc/ols/2006/ols2006v2-pages-59-72.pd...
i_am_a_peasant 4y ago
> Nothing saves you from kill -9, as we all know. You making a syscall and getting the kernel stuck somewhere and having your process in a D state will keep you alive ;D.
bheadmaster 4y ago
> Nothing saves you from kill -9, as we all know. True, but it doesn't have to be you who does the cleanup. You could create a background process and establish a temporary UNIX socket connection, so when the parent dies, the socket closes and the child process cleans up everything.

by chasil 4y ago

bombcar 4y ago

I wonder if the fact that you can delete a file and still access its contents as long as a file descriptor is still open would allow some dorty magic. Probably not because iirc you can create a file with the same name right after deletion even if a fd is open to the old one.

chasil 4y ago
SQLite will open temporary files (for sorting and sundry functions), then immediately unlink() them. This is allowed behavior under POSIX. The NFS trick was documented in "Why NFS Sucks" by Olaf Kirch. "Some other cases are a bit stranger. One such case is the ability to write to an open unlinked file. POSIX says an application can open a file for reading and writing, unlink it, and continue to do I/O on it. The file is not supposed to go away until the last application closes it. "This is difficult to do over NFS, since traditionally, the NFS server has no concept of “open” files (this was added in NFSv4, however). So when a client removes a file, it will be gone for good, and the file handle is no longer valid— and attempt to read from or write to that file will result in a “Stale file handle” error. "The way NFS traditionally kludges around this is by doing what has been dubbed a “silly re- name.” When the NFS client notices during an unlink call that one or more applications still hold an open file descriptor to this file, it will not send a REMOVE call to the server. Instead, it will rename the file to some temporary file name, usually .nfsXXX where XXX is some hex number. This file will stay around until the last application closes its open file descriptor, and only then will the NFS client send the final REMOVE call to the server that gets rid of this renamed file. "This sounds like a rather smart sleight of hand, and it is—up to a point. First off, this does not work across different clients. But that should not come as a surprise given the lack of cache consistency." https://www.kernel.org/doc/ols/2006/ols2006v2-pages-59-72.pdf https://www.kernel.org/doc/ols/2006/ols2006v2-pages-59-72.pd...

i_am_a_peasant 4y ago

> Nothing saves you from kill -9, as we all know. You making a syscall and getting the kernel stuck somewhere and having your process in a D state will keep you alive ;D.

bheadmaster 4y ago

> Nothing saves you from kill -9, as we all know. True, but it doesn't have to be you who does the cleanup. You could create a background process and establish a temporary UNIX socket connection, so when the parent dies, the socket closes and the child process cleans up everything.