in reply to Log Rotation

One gotcha you need to be aware of, (on *NIX at least), if your application/daemon still has the logfile open for writing your rename in line 28/31 will not remove that association. Instead, the application will continue writing to the logfile.1 and will do so until you eventually remove it, so you might end up losing data between the tar and the rm (consider using the Perl builtin unlink here instead BTW). Also, your application might get confused if the file it is writing to (and for which it holds a valid open file descriptor) suddenly vanishes underneath it.

One method of dealing with this is to send a HUP signal to the application (provided you know which process it is and can figure out the process id) after renaming the file. Most long-running daemons take that as a signal to reopen log files and will do the right thing. You could also figure out which processes have an open file descriptor on the log file (by using the *NIX utility lsof for example) and then send a SIGHUP to that process. Or use one of the modules andreas1234567 pointed out, they have methods for dealing with this exact problem.

Lastly, a non-perl method: take a look at logrotate, it's a common utility used for rotating logs with all bells and whistles built in.


All dogma is stupid.

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Re^2: Log Rotation
by Danikar (Novice) on Nov 23, 2007 at 17:09 UTC
    Thanks, I will probably go ahead and use logrotate for this particular situation. Though, I'll still continue on my perl script for fun =).
[reply]
      I will sometimes try to reinvent the wheel. Here is my effort. I wrote this several years ago, before I learned to love CPAN and stop reinventing the wheel. I added the syslog piece recently when I was testing Sys::Syslog for inclusion in other programs I am working on. A disclaimer - I do not use this in production. 
      package MyMods::Log::Logroll;

use strict;
use warnings;
use Sys::Syslog;
use Carp;

our $VERSION = '0.01';

# Syslogging...
my $slog = \&do_syslog;

my %config = ();

sub new
{
    %config = @_;
    confess "Baselog not defined" unless $config{'baselog'};

    $config{'maxbytes'} = 102400 unless $config{'maxbytes'};
    $config{'maxlogs'}  = 5 unless $config{'maxlogs'};
    $config{'UID'} =  ( exists $config{'strict'} == 1 ) ? $< : $>;

    #return ( &rollit() == 0 ) ? 0 : 1;
}

sub roll
{
    my $logowner;
    my $filebytes;

    my $last = $config{'maxlogs'}; 

    if ( -f $config{'baselog'} and ! -x $config{'baselog'} )
    {
        #  0 dev      device number of filesystem
        #  1 ino      inode number
        #  2 mode     file mode  (type and permissions)
        #  3 nlink    number of (hard) links to the file
        #  4 uid      numeric user ID of file's owner
        #  5 gid      numeric group ID of file's owner
        #  6 rdev     the device identifier (special files only)
        #  7 size     total size of file, in bytes
        #  8 atime    last access time in seconds since the epoch
        #  9 mtime    last modify time in seconds since the epoch
        # 10 ctime    inode change time in seconds since the epoch (*)
        # 11 blksize  preferred block size for file system I/O
        # 12 blocks   actual number of blocks allocated
        my @info = stat($config{'baselog'});
        $logowner = $info[4];
        $filebytes = $info[7];
    }
    else
    {
        $slog->("$config{'baselog'} is NOT a regular file");
        return 1;
    }
    
    # File has not reached $maxbytes yet.
    return 0 if $config{'maxbytes'} > $filebytes;
    
    # obviously root can do anything
    if ( ! $config{'UID'} == $logowner and ! $config{'UID'} == 0 )
    {
        $slog->("uid $config{'UID'} is trying to logroll $config{'base
+log'} (owner is $logowner)");
        return 1;
    }    
    
    while ( $last > 1 )
    {
       $last--;
       $slog->("renaming $config{'baselog'}");
       rename_logs($last);
    }
    
    if ( -e $config{'baselog'} ) 
    {
        rename( "$config{'baselog'}", "${config{'baselog'}}_1" ); 
        $slog->("Error renaming $config{'baselog'} -> ${config{'baselo
+g'}}_1")
            unless -e "${config{'baselog'}}_1";
    }

    return ( touchfile() == 0 ) ? 0 : 1;
}    

sub touchfile
{
    my $BASELOG;
    unless ( open $BASELOG, ">$config{'baselog'}" )
    {
         $slog->("Unable to open $config{'baselog'}");
         return 1;
    }
    return ( close $BASELOG ) ? 0 : 1;
}

sub rename_logs
{
     my $x = shift;
     my $y = $x + 1;

     if ( -e "${config{'baselog'}}_$x" )
     {
        $slog->("renaming ${config{'baselog'}}_$x -> ${config{'baselog
+'}}_$y"); 

        rename("${config{'baselog'}}_$x", "${config{'baselog'}}_$y");

        my $return = ( -e "${config{'baselog'}}_$y" ) ? 0 : 1;

        $slog->("Error renaming ${config{'baselog'}}_$x -> ${config{'b
+aselog'}}_$y")
            unless $return == 0;

        return $return;
     }
}

sub do_syslog
{
    my $message = shift;

    openlog( $0, "ndelay,pid", "local0");
    syslog("info", $message);
    closelog;
}

1;

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      Ted
      --
      "That which we persist in doing becomes easier, not that the task itself has become easier, but that our ability to perform it has improved."
        --Ralph Waldo Emerson
[reply]
[d/l]

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