It shows the files in split views and you can even show different files in different rows and columns. What's the big deal? The tail command can also do the same, right?īut Multitail has some advantage over the conventional tail command. Multitail, as the name suggests, is used to display multiple files at once. Method 2: Monitor multiple log files at once with multitail There is a slightly better way to view multiple log files at once using a utility called multitail. You'll see that it starts showing the real time changes along with the file name before it so that you can distinguish between different log sources. Just provide the path of the file in this manner: tail -f log_file_1 -f log_file_2 You can monitor multiple log files at the same time with the tail command. Tail is nice for monitoring a log file in real time but what if you have to analyze more than one log files at the same time? The answer lies in the next section. The next time you tail a log file, use it this way to monitor it more effectively. tail -follow=name log_file | grep -C 3 -i - E 'search_term_1|search_term_2' This way, even when log rotation takes place, the tail will be pointing to the current log file (because its name never changes). The solution is to follow a log file by its name. If the current log file is rotated, tail command will now be pointing to an archived log file which will not be recording any change now. By default, the tail command works on the file descriptor. That creates a problem if you are tailing a log file in real time. This means that after the current log file reaches a certain size, it is renamed and zipped. If you are working on an enterprise server, chances are that logs are rotated. Want to make it even better? You can grep on multiple search term and even make it a case insensitive search: tail -f log_file | grep -C 3 -i - E 'search_term_1|search_term_2' Tailing the file with log rotation This will give a better perspective on what's happening. Now, you'll see the lines matching the search term along with 3 lines before and after it. This is why I use grep command to show a few lines before and after the searched term with option -C. I have often found that just the lines with searched terms don't reveal the necessary details. This is good, right? Let's make it a bit better. To make things easier, combine the tail and grep command like this: tail -f log_file | grep search_term Finding that in the flood of incoming new lines is close to impossible. You'll often be looking for a particular term when monitoring the log file. But watching the log file continuously when there are so many rapid changes happening in real time is not very helpful. Tail and grepĪlright! So the tail command solves a problem by showing the file changes in real life. To stop the tailing of the log file, use Ctrl+C terminal shortcut. You can use the -f option to follow the tail of a file, which means that it will keep on showing the new lines added to the file continuously. The tail command is essentially used for showing the lines of a file from the end and hence the term 'tail'. The tail command is so popular for viewing log files in real life that sysadmins use the term 'tail the log file'. Method 1: Watch log files with the tail command How do you see the content of log files in real time? Tail is the most popular command for this purpose but there are some other tools as well. To monitor logs, you need to watch the log file as its content changes. But log files are dynamic and their content change with time. That's good for files that has static content. You use cat command or probably less command for this purpose. 2805 static void _sched _schedule(void)Ģ871 next->_start_ts = (next->_ts).tv_sec * 1000 + (next->_ts).You know how to view files in Linux. We also need to add some other source codes before context switch in core.c like following. In above source codes, ‘enable_flag’ controls whether to output the timeslice and ‘enable_pid’ controls which process’s timeslice to be outputed, which can be controled in userspace (“/sys/module/core/parameters/enable_flag” and “/sys/module/core/parameters/enable_pid”) by users/developers. The way to export them in ‘linux-3.16.39/kernel/sched/core.c’ is as follows. Firstly, you need to export two flags from Linux kernel so that you can control them to output which process’s (PID) timeslice.
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