What I dont understand is if the file is zeroed ( >file) how come it the next minute be greater than previously...
Quote:
Originally Posted by MadeInGermany
tells that the O_APPEND flag in open() jumps to the end of the (with the old file size) prior to every write.
That's incorrect. Before each write(), O_APPEND sets the descriptor's offset to the current end of file. If a file opened with O_APPEND is truncated to 0 size, the next write would see that and would place its bytes at the beginning of the file.
What we're seeing here is the absence of O_APPEND. Truncation does not affect the offsets of open file descriptions, so, without O_APPEND, writes continue where they had been located before truncation; file size is restored with null bytes replacing what had been truncated.
Regards,
Alister
These 3 Users Gave Thanks to alister For This Post:
Greetings, I just started using scripting languages,
im trying to get a tcpdump in a file, change the
file name every 5mins ... this is what i have but its
not working ... any suggestions?
#!/bin/bash
# timeout.sh
#timestamp format
TIMESTAMP=`date -u "+%Y%m%dT%H%M%S"`
#tdump =`tcpdump... (3 Replies)
Hello,
I only know the basic for shell programing. I need help for this, I thinks this is a basic for anyone who know a litle of shell scripting.
I need creat a script for a rotatate logs, when a filesystem is full. I have a filesystem.
The rotate consist in zip the current log (copy) and... (1 Reply)
Hello All,
I am learning unix and basically I want to rotate one of my application logs every 1 hour. I need to rotate that file every one hour. I looked in the forums and googled.. but couldn;t get proper information. Requesting you all to kindly guide me.
Our application is running on... (4 Replies)
Hi all,
Am trying to write my own log rotate script. Curremtly, what I have is as below:
#!/bin/ksh
file_to_rotate=${1}
x=${2}
while ]
do
let curr=${x}
let prev=${x}-1
if ] ; then
#echo "cp -p ${file_to_rotate} ${file_to_rotate}.${curr}"
cp -p... (7 Replies)
Hi Experts,
I have script on crontab and give output quite large. I would like to know how to create rotate log when the size of log maximum 50MB
if the test.log is 50MB then create test.0
Thanks
Edy (2 Replies)
Hi,
I have below script in logrotate.d to rotate logs.
logs are not rotating after the file grow to 1k, do you have any idea? Is it because of it just only 1K?
Please let me know if the below syntax is in correct.
# more trotate
/sourcepath/*/servers/*/logs/*log... (2 Replies)
My problem: Both access and error logs do not rotate any more and get really large.
They are located here: /srv/www/+vHost name here+/logs/
Configuration seems to be here:
/etc/logrotate.conf => looks OK, including "size 10M" to avoid large files
(/etc/logrotate.d => is empty)
manually... (4 Replies)
Discussion started by: floko
4 Replies
LEARN ABOUT LINUX
pwrite64
PREAD(2) Linux Programmer's Manual PREAD(2)NAME
pread, pwrite - read from or write to a file descriptor at a given offset
SYNOPSIS
#include <unistd.h>
ssize_t pread(int fd, void *buf, size_t count, off_t offset);
ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
pread(), pwrite():
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
DESCRIPTION
pread() reads up to count bytes from file descriptor fd at offset offset (from the start of the file) into the buffer starting at buf. The
file offset is not changed.
pwrite() writes up to count bytes from the buffer starting at buf to the file descriptor fd at offset offset. The file offset is not
changed.
The file referenced by fd must be capable of seeking.
RETURN VALUE
On success, pread() returns the number of bytes read (a return of zero indicates end of file) and pwrite() returns the number of bytes
written.
Note that it is not an error for a successful call to transfer fewer bytes than requested (see read(2) and write(2)).
On error, -1 is returned and errno is set to indicate the cause of the error.
ERRORS
pread() can fail and set errno to any error specified for read(2) or lseek(2). pwrite() can fail and set errno to any error specified for
write(2) or lseek(2).
VERSIONS
The pread() and pwrite() system calls were added to Linux in version 2.1.60; the entries in the i386 system call table were added in
2.1.69. C library support (including emulation using lseek(2) on older kernels without the system calls) was added in glibc 2.1.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
NOTES
The pread() and pwrite() system calls are especially useful in multithreaded applications. They allow multiple threads to perform I/O on
the same file descriptor without being affected by changes to the file offset by other threads.
C library/kernel differences
On Linux, the underlying system calls were renamed in kernel 2.6: pread() became pread64(), and pwrite() became pwrite64(). The system
call numbers remained the same. The glibc pread() and pwrite() wrapper functions transparently deal with the change.
On some 32-bit architectures, the calling signature for these system calls differ, for the reasons described in syscall(2).
BUGS
POSIX requires that opening a file with the O_APPEND flag should have no effect on the location at which pwrite() writes data. However, on
Linux, if a file is opened with O_APPEND, pwrite() appends data to the end of the file, regardless of the value of offset.
SEE ALSO lseek(2), read(2), readv(2), write(2)Linux 2017-09-15 PREAD(2)