Create log file in linux

Best answer: How do I create a log file in the linux script?

To write the output of the Bash command to the log file, you can use right angle bracket symbol (>) or double right angle symbol (>>). Right angle brake symbol (>): Used to write the output of a bash command to a disk file. If the file is not already present, it creates one with the specified name.

How do I create a log file on Linux?

2 answers. Single cat >> custom. Log in . >> means add to the end of the file instead of >, which would remove the contents of the file and then write the message.

How do I create a log file?

To create a log file in Notepad:

1. Click Start, point to Programs, point to Accessories, and then click Notepad.
2. Write . LOG on the first line and then press ENTER to move to the next line.
3. On the File menu, click Save As, type a descriptive name for your file in the File Name box, and then click OK.

How do I save a log file in Linux?

Linux systems usually keep their log files in the /var/log directory. This works fine, but check if the app is saved to a specific directory in /var/log. If it does, great. If not, you may want to create a dedicated directory for the application in /var/log.

How do you write a script file?

How to create a file in Linux from the terminal window?

1. Create an empty text file called foo.txt: tap foo.bar. …
2. Create a text file on Linux: cat > filename.txt.
3. Add data and press CTRL + D to save the filename.txt when using cat on Linux.
4. Run the shell command: echo ‘This is a test’ > data.txt.
5. Add text to existing file on Linux:

How do I run a shell script?

Steps to write and run a script

1. Open the terminal. Go to the directory where you want to create your script.
2. Create a file with . sh.extension
3. Write the script to the file using an editor.
4. Make the script executable with the chmod +x command .
5. Run the script using ./ .

What is the log file in Linux?

The log files are a set of logs that Linux maintains for administrators to keep track of important events. They contain messages about the server, including the kernel, services, and applications running on it. Linux provides a centralized repository of log files that can be located in the /var/log directory.

How do I list all processes in Linux?

Check running process in Linux

1. Open the terminal window on Linux.
2. For the remote Linux server, use the ssh command to login.
3. Type the ps aux command to see the entire running process on Linux.
4. Alternatively, you can issue the top command or the htop command to view the running process on Linux.

How do I view a log file?

You can read a LOG file with any text editor, such as Windows Notepad. You may also be able to open a LOG file in your web browser. Just drag it directly into the browser window or use the keyboard shortcut Ctrl+O to open a dialog box to find the LOG file.

What is a log txt file?

record» and «. txt» are extensions both plain text files. . LOG files are usually generated automatically, while . TXT files are created by the user. For example, when a software installer runs, it might create a log file that contains a record of the files that were installed.

What is the log file in the database?

The log files are the main data source for network observability. A log file is a computer-generated data file that contains information about usage patterns, activities, and operations within an operating system, application, server, or other device.

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Write to custom log file from a Bash script

In Linux, I know how to write a simply message to the /var/log/messages file, in a simple shell script I created:

I want to stop throwing messages into the default /var/log/messages file, and create my own. I tried this:

#!/bin/bash logger "have more fun" > /var/log/mycustomlog 

It still logs to /var/log/messages . It did create the /var/log/mycustomlog , but it’s empty. Anyone see what I’m missing?

Redirecting standard output doesn’t work because logger doesn’t write to standard output; it writes to the file configured by syslog(3) to receive log messages.

5 Answers 5

logger logs to syslog facilities. If you want the message to go to a particular file you have to modify the syslog configuration accordingly. You could add a line like this:

and restart syslog. Then you can log like this:

logger -p local7.info "information message" logger -p local7.err "error message" 

and the messages will appear in the desired logfile with the correct log level.

Without making changes to the syslog configuration you could use logger like this:

logger -s "foo bar" >> /var/log/mycustomlog 

That would instruct logger to print the message to STDERR as well (in addition to logging it to syslog), so you could redirect STDERR to a file. However, it would be utterly pointless, because the message is already logged via syslog anyway (with the default priority user.notice ).

For anyone else who was confused at the use of the number 2 after the string in the last example, 1 redirects stdout, and 2 redirects stderr. More info available here: tldp.org/LDP/abs/html/io-redirection.html

And for anyone who doesn’t know how to edit the syslog configuration, here it is on Ubuntu: askubuntu.com/questions/42152/where-is-syslog-conf

What does the — before the file path indicate? I’ve tried googling around but can’t find anything about it. Is it required?

@chepner make a good point that logger is dedicated to logging messages.

I do need to mention that @Thomas Haratyk simply inquired why I didn’t simply use echo .

At the time, I didn’t know about echo, as I’m learning shell-scripting , but he was right.

My simple solution is now this:

#!/bin/bash echo "This logs to where I want, but using echo" > /var/log/mycustomlog 

The example above will overwrite the file after the >

So, I can append to that file with this:

#!/bin/bash echo "I will just append to my custom log file" >> /var/log/customlog 

• on a side note, it’s simply my personal preference to keep my personal logs in /var/log/ , but I’m sure there are other good ideas out there. And since I didn’t create a daemon, /var/log/ probably isn’t the best place for my custom log file. (just saying)

I agree that this is a good approach but the log file will keep growing and there is no mechanism of archiving or deleting old logs. If you log frequently, then this can take considerable amount of storage.

There’s good amount of detail on logging for shell scripts via global varaibles of shell. We can emulate the similar kind of logging in shell script: http://www.cubicrace.com/2016/03/efficient-logging-mechnism-in-shell.html The post has details on introdducing log levels like INFO , DEBUG, ERROR. Tracing details like script entry, script exit, function entry, function exit.

If you see the man page of logger:

LOGGER(1) BSD General Commands Manual LOGGER(1)

NAME logger — a shell command interface to the syslog(3) system log module

SYNOPSIS logger [-isd] [-f file] [-p pri] [-t tag] [-u socket] [message . ]

DESCRIPTION Logger makes entries in the system log. It provides a shell command interface to the syslog(3) system log module.

It Clearly says that it will log to system log. If you want to log to file, you can use «>>» to redirect to log file.

This is an incorrect interpretation of the man page. logger uses syslog or (in the case of most Linux systems) rsyslog which can be configured to place log messages where ever you like.

I did it by using a filter. Most linux systems use rsyslog these days. The config files are located at /etc/rsyslog.conf and /etc/rsyslog.d .

Whenever I run the command logger -t SRI some message , I want «some message» to only show up in /var/log/sri.log .

To do this I added the file /etc/rsyslog.d/00-sri.conf with the following content.

# Filter all messages whose tag starts with SRI # Note that 'isequal, "SRI:"' or 'isequal "SRI"' will not work. # :syslogtag, startswith, "SRI" /var/log/sri.log # The stop command prevents this message from getting processed any further. # Thus the message will not show up in /var/log/messages. # & stop 

Then restart the rsyslogd service:

systemctl restart rsyslog.service 

Here is a shell session showing the results:

[root@rpm-server html]# logger -t SRI Hello World! [root@rpm-server html]# cat /var/log/sri.log Jun 5 10:33:01 rpm-server SRI[11785]: Hello World! [root@rpm-server html]# [root@rpm-server html]# # see that nothing shows up in /var/log/messages [root@rpm-server html]# tail -10 /var/log/messages | grep SRI [root@rpm-server html]# 

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Unix syslog is a host-configurable, uniform system logging facility. The system uses a centralized system logging process that runs the program /etc/syslogd or /etc/syslog. The operation of the system logger is quite straightforward.

What is Unix system log?

Unix syslog is a host-configurable, uniform system logging facility. The system uses a centralized system logging process that runs the program /etc/syslogd or /etc/syslog. The operation of the system logger is quite straightforward.

Where are system logs in Unix?

Linux logs can be viewed with the command cd/var/log, then by typing the command ls to see the logs stored under this directory. One of the most important logs to view is the syslog, which logs everything but auth-related messages. Jun 23, 2017

What is system log in Linux?

Log files are a set of records that Linux maintains for the administrators to keep track of important events. They contain messages about the server, including the kernel, services and applications running on it. Apr 19, 2020

Where can I find system logs in Linux?

Linux has a special directory for storing logs called /var/log . This directory contains logs from the OS itself, services, and various applications running on the system.

What is system Logging?

The system log (syslog) contains a record of the operating system (OS) events that indicates how the system processes and drivers were loaded. The syslog shows informational, error and warning events related to the computer OS.

What is Unix syslog?

Syslog, is a standardized way (or Protocol) of producing and sending Log and Event information from Unix/Linux and Windows systems (which produces Event Logs) and Devices (Routers, Firewalls, Switches, Servers, etc) over UDP Port 514 to a centralized Log/Event Message collector which is known as a Syslog Server. Aug 19, 2021

How do you create a log file in Unix?

To write output of Bash Command to Log File, you may use right angle bracket symbol (>) or double right angle symbol (>>). Right angle braketsymbol (>) : is used to write output of a bash command to a disk file. If the file is not already present, it creates one with the name specified. Dec 15, 2017

How do I open a log file in PuTTY?

Double-click the PuTTY icon on your Desktop to open it or search your Start menu. Connect to your server. Enter your hostname (or IP address), port number, and password to connect to your server with PuTTY. Navigate the PuTTY window to your logs. May 11, 2021

How do I view a log file?

You can read a LOG file with any text editor, like Windows Notepad. You might be able to open one in your web browser, too. Just drag it directly into the browser window, or use the Ctrl+O keyboard shortcut to open a dialog box to browse for the file. Oct 15, 2021

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