6/11/2023 0 Comments Linux file copy log outWhen the cp program wants to write to the file it gets a reference to it from the directory, writes a length of zero into the metadata stored in the directory (this is a slight simplification) and gives up the handle. In this case the program that opened it and the directory it was opened 'in' hold references to the file. In Linux (actually all unicies) files are created when they are opened and deleted when nothing holds a reference to them. This just goes to show that when you use one particular technique for other (valid) purposes, adapting it to yet another is not necessarily the simplest mechanism - even though it works. Use append redirection rather than the wrapper (' cantrip') code above. Open("/platform/SUNW,Ultra-4/lib/libc_psr.so.1", O_RDONLY) = 3 Open("/usr/lib/libsocket.so.1", O_RDONLY) = 3 Open("/usr/lib/libcurses.so.1", O_RDONLY) = 3 Open("/var/ld/ld.config", O_RDONLY) Err#2 ENOENT If (argc >' is the append operator - and indeed, on Solaris 10, bash (version 3.00.16(1)) does use the O_APPEND flag - thereby making the code above unnecessary, as shown ('Black JL:' is my prompt on this machine): Black JL: truss -o uss bash -c "echo Hi > x3.29" #include įprintf(stderr, " (%d: %s)", errnum, strerror(errnum)) This code rigs standard output so it is in O_APPEND mode and then invokes the command given by its arguments (rather like nice runs a command after adjusting its nice-level, or nohup runs a command after fixing things so it ignores SIGHUP). This means that after you truncate the file, the next write will implicitly seek to the end of the file (meaning back to offset zero) and then write the new information. Ideally, you should ask the vendor of the application to open the log file with the O_APPEND flag. When it writes again, the file system treats the start of the file as all zero bytes - without actually writing the zeroes to disk. This happens because the file is truncated to zero length, but the file descriptor in the application still points immediately after its last write. The interesting thing about those regrown files is that the first 128 KB or so will be all zeroes after you truncate the file by copying /dev/null over it.
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