What are the commands to view logs in Linux?

Linux commands to view logs are: 1. tail command, used to view the previous lines of logs; 2. head command, used to view the following lines of logs; 3. cat command, which can be used to query keywords log.

#The operating environment of this article: linux5.9.8 system, Dell G3 computer.

What are the commands for viewing logs in Linux?

Common commands for viewing logs in Linux

1. Common commands for viewing logs

tail:

-n is the display line number; equivalent to the nl command; the example is as follows:

tail -100f test.log Real-time monitoring of 100 lines of log

tail -n 10 test.log Query the tail of the log The last 10 lines of logs;

tail -n 10 test.log Query all logs after 10 lines;

head:

It is the opposite of tail, tail is to look at How many lines of logs are there after; the example is as follows:

head -n 10 test.log Query the first 10 lines of logs in the log file;

head -n -10 test.log Query the log file except the last All other logs in the 10th line;

cat:

tac is viewed in reverse order, and the word cat is written in reverse; the example is as follows:

cat -n test.log |grep " debug" Query keyword logs

2. Application scenario 1: View by line number---Filter out logs near the keyword

1) cat -n test.log | grep "debug" Get the line number of the key log

2) cat -n test.log | tail -n 92|head -n 20 Select the middle where the keyword is located A line. Then check the log in this keyword front 10 lines and 10 lines:

TAIL -N 92 to indicate the log of the query 92 lines

Head -N 20 Check the first 20 records in the results

3. Application scenario 2: query logs based on date

sed -n '/2014-12 -17 16:17:20/,/2014-12-17 16:17:36/p' test.log

Special note: The two dates above must be the logs printed in the log, otherwise Invalid;

                    1. First grep '2014-12-17 16:17:20' test.log to determine whether there is this time point in the log

 

4 .Application scenario three: The log content is very large and it is inconvenient to view it when printed on the screen

(1) Use the more and less commands,

Such as: cat -n test.log | grep "debug" |more This will print in pages. Click the space bar to turn pages

(2) Use >xxx.txt to save it to a file. You can then pull down the file for analysis

For example: cat -n test.log |grep "debug" >debug.txt

Recommended study: "linux video tutorial"

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