Linux Tips

As the name suggests, grep or global regular expression print lets you search for specific text patterns within a file’s contents. Its functionalities include pattern recognition, defining case sensitivity, searching multiple files, recursive search, and many more. 

So whether you’re a beginner or a system administrator, knowing about the grep command to locate the files efficiently is good. This tutorial will explain how to use grep in Linux and discuss its different applications.

How To Use Grep Command in Linux

The basic function of the grep command is to search for a particular text inside a file. You can do that by entering the following command:

Please replace ‘text_to_search’ with the text you want to search for and ‘file.txt’ with the target file. For example, to find the string “Hello” in the file named file.txt, we will use:

On entering the above command, grep will scan the Intro.txt file for “Hello.” As a result, it shows the output of the whole line or lines containing the target text.

If the target file is on a path different from your current directory, please mention that path along with the file name. For instance:

Here, the tildes ‘~’ mark represents your home directory. The above example shows how you can search for a piece of text in a single file. However, if you want to do the same search on multiple files at once, mention them subsequently in one grep command:

In case you’re not sure about your string’s cases(uppercase or lowercase), perform a case-insensitive search by using the i option:

Although the string we input was not the exact match, we received accurate results through the case-insensitive search. In case you want to invert the changes and check files that don’t contain the specific pattern, then please use the v option:

Moreover, if you want to display the lines that start with a certain word, use the ‘^’ symbol. It serves as an anchor that specifies the beginning of the line.

The above commands will only be useful when you know which file to search. In this case, you can recursively search the string inside the whole directory using the r option. For example, let’s search “Hello” inside the Documents directory:

Furthermore, you can also count the number of times the input string appears in a file through the c option:

Similarly, you can display the line numbers along with the matched lines with the n option:

A Quick Wrap-up

Users often remember that a file used to contain a piece of text but forget the file name, which can land them in deep trouble. Hence, this tutorial was about using the grep command to search for text in a file’s contents. Furthermore, we have used different examples to demonstrate how you can tweak the grep command’s functioning with a few options. You can experiment by combining multiple options to find out what suits best according to your use case.

Linux works well as a multiuser operating system. Many users can access a single OS simultaneously without interpreting each other. However, if others can access your directories or files, the risk may increase. 

Hence, from a security perspective, securing the data from others is essential. Linux has features to control access from permissions and ownership. The ownership of files, folders, or directories is categorized into three parts, which are:

• User (u): This is the default owner, also called the file’s creator.
• Group (g): It is the collection of multiple users with the same permissions to access folders or files. 
• Other (o): Those users not in the above two categories belong to it. 

That’s why Linux offers simple ways to change file permissions without hassles. So in this quick blog, we have included all the possible methods to change file permissions in Linux. 

How to Change File Permissions in Linux

In Linux, mainly Linux file permissions are divided into three parts, and these are:

• Read (r): In this category, users can only open and read the file and can’t make any changes to it. 
• Write (w): Users can edit, delete, and modify the file content with written permission.
• Execute (x): When the user has this permission, they can execute the executable script and access the file details.

As you can see from the above table, there are two types of symbol representation of permission. You can use both of these modes (symbolic and absolute) to change file permissions using the chmod command. The chmod refers to the change mode that allows users to modify the access permission of files or folders.

Using chmod Symbolic Mode

In this method, we use the symbol (for owner- u, g, o; for permission- r, w, x) to add, subtract, or set the permissions using the following syntax:

Before changing the file permission, first, we need to find the current one. For this, we use the ‘ls’ command.

Here the permission symbols belong to the following owner:

• ‘-‘ : shows the file type.
• ‘rw-‘ : shows the permission of the user (read and write)
• ‘rw-‘ : shows the permission of the group(read and write)
• ‘r- -‘ : shows the permission of others (read)

In the above image, we highlighted one file in which the user has read and write permission, the group has read and write permission, and the other has only read permission. So here, we are going to add executable permission to others. For this, use the following command:

As you can see, the execute permission has been added to the other category. Simultaneously, you can also change the multiple permissions of different owners. Following the above example, again, we change the permissions in it. So, here, we add executable permission from the user, remove write permission from the group, and add write permission to others. For this, we can run the below command:

Note: Use commas while separating owners, but do not leave space between them.

Using chmod Absolute Mode

Similarly, you can change the permission through absolute mode. In this method, mathematical operators (+, -, =) and numbers represent the permissions, as shown in the above table. For example, let’s take an example and the updated permission of the file data is as follows:

Mathematical representation of the permission:

Now, we are going to remove read permission from the user and others, and the final calculation is:

To update the permission, use the following chmod command:

Change User Ownership of the File

Apart from changing the file permission, you may also have a situation where you have to change the file ownership. For this, the chown is used which represents the change owner. 

The file details represent the following details:

So, in the above example, the owner’s or user name is ‘prateek’, and you can change the user name that only exists on your system. Before changing the username, first list all the users using the following command:

Or

Now, you can change the username of your current or new file between these names. The general syntax to change the file owner is as follows:

Note: Sudo permission is required in some cases.

Based on the above result, we want to change the username from ‘prateek’ to ‘proxy.’ To do this, we run the below command in the terminal:

Change Group Ownership of the File

First, list all the groups that are present in your system using the following command:

The  ‘chgrp’ command (change group) changes the filegroup. Here, we change the group name from ‘prateek’ to ‘disk’ using the following command:

Conclusion

Managing file permissions is essential for access control and data security. In this guide, we focused on changing the file permissions in Linux. It has a feature through which you can control ownership (user, group, others) and permissions (read, write, execute). Users can add, subtract, or set the permissions according to their needs. Users can easily modify the file permissions through the chmod command using the symbolic and absolute methods. 

Operating systems use packets for transferring the data on a network. These are small chunks of information that carry data and travel among devices. Moreover, when any network problem arises, packets aid in identifying the root cause of the underlying problem. How? By tracing the route of those packets.

The traceroute command in Linux helps you map the path packets take while traveling to a specific destination. This further helps you troubleshoot network latency, packet loss, network hops, DNS resolution issues, slow website access, and more. So, in this blog, we will explain simple ways to use the traceroute command in Linux.

How To Use Traceroute Command in Linux

Firstly, the traceroute does not come preinstalled in many Linux distributions. However, you can install it by executing one of the below command according to your system: 

After installation, you can implement the traceroute command by entering:

Replace <destination_IP> with the device’s IP address at the destination. Once you run the command, your system will display the list of hops with the IP address and response time. Hops are the devices that your packets go through while traveling to a specific destination. For example, let’s use the traceroute command for Google’s IP address:

The result shows only one hop while marking others as an asterisk(*). This happens because the subsequent hops did not respond within the timeout period of 3 seconds. Moreover, the traceroute command, by default, uses DNS resolution to get the hostnames of hops, which slows down the process. You can omit that part and guide it to display only the IP addresses by using the -n option:

If you want to limit the number of hops, use the -m option along with the traceroute command:

Here, put the desired number of hops in place of N. On execution, it will return only N number of hops in the results. The traceroute command only displays every hop’s round-trip time(RTT). However, you can get more detailed timing information with the -I option:

This command sends an ICMP echo request to retrieve more accurate RTT data. For instance, retake the example of Google:

Tip: If your specified destination restricts ICMP packets, you can instead trace the UDP packets by employing the -U option:

In case you want to explore more options for traceroute, then please run the below command: 

A Quick Wrap-up

Traceroute is an amazing CLI utility that you can use to diagnose network-related issues in Linux. It traces the path of packets to identify all the critical issues of the network. Hence, We have explained every single detail about the traceroute command with the help of some examples. 

The htop is a CLI utility to check an interactive list of running processes in real-time. It is a more feature-rich and user-friendly alternative to the top command. The htop command allows you to manage system processes, monitor resources, and perform other administration tasks.

One of the most prominent features of htop is that it shows color-coded processes, which helps you differentiate them based on resource usage. Furthermore, it lets you customize the results with its sort and filter options. So, this short tutorial is about how to use the htop command in Linux without hassles. Unlike top, the htop command is not preinstalled in most Linux systems. That’s why you must install it using the following commands:

Now, you can use the htop command, so let’s start with the basics:

When you execute the above command, it launches the htop utility. Here, you can use the arrow keys to navigate up and down the processes. Moreover, press ‘F1’ or ‘?’ to get the help screen for additional navigation shortcuts.

Sort Processes in htop

In htop, you can sort the processes by CPU, memory, and other usage. Open the sorting menu by pressing F6:

For example, select the PERCENT_CPU option and press ‘Enter.’

As you can see in the above image, all the processes are now sorted by CPU consumption. 

Search and Filter Processes in htop

To search any process in htop, please go through the following steps:

Press ‘F3’ to open the search bar.

Similarly, press ‘F4’ to filter out the processes.

Additional Options with htop

-d, –delay=[argument]: By default, htop updates the processes every second, but you can add a delay using this option. For instance, to introduce a delay of 10 seconds, we would enter ‘–delay=10.’

-C, –no-color: This option disables the color output, which is helpful in systems with limited terminal support for colors.

-u, –user=[username]: To display the processes for a specific user. Just replace ‘[username]’ with the target user’s name.

-p, –pid=[PID1,PID2]: Displays information for specified process IDs. For example, let’s check the details of PID 1:

-v, –version: Prints htop version information.

-h, –help: This displays a help message with usage information.

Kill a Process in htop

If you want to kill any process, select it and press the ‘F9’ key or ‘k’ to transmit a kill signal for the selected process.

Wrapping Up

Htop is a powerful utility for interactively checking system processes in real time. This tutorial briefly discusses how to use the htop command. As htop is not a preinstalled utility in Linux distributions, your first step is to install it using the mentioned commands. Later, we explained how to sort, search, filter, and kill processes from the htop utility.

All UNIX-based operating systems, including Linux, follow the structure that “everything is a file.” These systems treat all the regular files, directories, processes, symbolic links, and devices like external hardware as files. You can create, modify, and delete files using the commands or from the File Manager.

Deleting files is essential when you accidentally create multiple files that become unnecessary for the system. So, in this quick blog, we will explain quick ways to delete a file in Linux with no trouble. There are a few methods of deleting the files, so let’s look at them individually with the correct examples. 

The rm Command

You can use the rm command to delete the file from the terminal. For example, you want to delete the “filename.txt” located in the Downloads directory, so first run the below command to open the directory in the terminal:

Then, use the following command:

The rm command doesn’t display any output, but you can use the -v option to get the output:

If you want to delete multiple files from the current directory, you can mention all those files in a single rm command. For example, to delete three files– file1.txt, file2.txt, file3.txt, please run the below command:

In case you want to delete all the files with the same extension, then you can run the following command: 

As the above image shows, we have deleted all the .txt files from the Downloads directory. Moreover, you can use multiple extensions in a single command to delete different types of files simultaneously. For example, let’s delete all the files having the .txt and the .sh extensions: 

Similarly, you can empty a directory by only adding the * in the rm command: 

Remember, the above command deletes all files except the directories. Hence, if there is a subdirectory, then the terminal will show the following output: 

However, you can use the -r option with the rm command to delete the subdirectories. The -r option recursively deletes the directory along with its contents:

In case you want to get the confirmation before deleting the file, please use the -i option. 

Once you run the command, the system will show a confirmation prompt, so all you have to do is press Y to delete or N to decline it. 

From the File Manager

We recommend deleting the file from the File Manager if you are a Linux beginner. So first open the File Manager and locate the directory: 

Now select the file and right-click it to get the context menu.

Finally, click on the Move to Trash option or press Delete button.

A Quick Wrap-up

Linux has various commands and methods to delete a file quickly. However, users must know how to delete files to maintain an organized system and minimal storage consumption. This quick tutorial explained two ways of doing so. Initially, we discussed how the rm command works, then explained briefly the step-by-step process of deleting files using the GUI.

The Logrotate utility simplifies the process of administering log files. It relocates and replaces log files to manage their size and organize them while maintaining the information present inside them. For example, it will maintain seven log files to keep daily records for seven days.

While rotating the log files, Logrotate deletes irrelevant old logs, preventing them from consuming excessive disk space. It runs periodically in the background to keep your systems organized and clean. So, if you want to learn about Logrotate, this blog is for you. Here, we have included in-depth information about how to set Logrotate on Linux.

How To Set Logrotate on Linux

Although many Linux distributions have Logrotate as the pre-installed utility. However, if your system does not have Logrotate, please use the following command to install it:

Now, let’s move to the configuration part. There are two kinds of logrotate configurations– global and system-specific. Open the ‘/etc/logrotate.conf’ file using a text editor. It is Logrotate’s primary configuration file, and any changes made to it will affect the whole system.

This file has three key sections:

1. To specify the rotation frequency, i.e., the time it should rotate the logs. It is set to weekly by default, but you can change it to daily, weekly, or monthly.
2. To define the number of rotated files it should keep, adjust the value based on how much historical data you want to retain. For instance, ‘rotate 4’ guides it to keep the latest four rotated log files and delete the earlier ones to free up disk space.
3. The third is to specify the permissions and ownership of the new log files it’ll create.

You can tweak these settings according to what suits your system best. For instance, to maintain weekly records for one month(28 days), you must enter:

This way, it will rotate one file weekly and keep four such files. Further, it creates a new log file for currently occurring events while giving the root user and group the read-and-write permissions and read-only for others.

If you have to monitor a specific application’s logs for underlying issues. In that case, you can tailor log rotation settings for that application by creating its separate logrotate configuration file. Let’s take an example of conda. First, create its file using:

In this file, add configurations specific to the conda logs:

Here, the compress command guides to compress the files so that resulting files take up less space. With the delaycompress command, you can hold the latest rotated file uncompressed to make it convenient for the users to refer to it.

The missingok option tells logrotate to ignore the absence of a log file and continue its operations without any error. At last, with notifempty, logrotate won’t rotate any empty log file. The logrotate should run automatically as per the default settings. However, you must confirm it using:

A Quick Wrap-up

Knowing the configuration process of the logrotate utility is crucial for system administrators and is also essential for disk management in Linux devices. Hence, this blog explains the approaches used to set logrotate on Linux. You can modify configurations globally and simultaneously change them for specific applications. Moreover, system-specific configurations should be used responsibly because they always override global settings.

However, many beginners don’t know the exact way to list the process without errors. So, in this short article, we will explain different methods to list the process in Linux. We have divided this section into multiple parts to give you the best commands to list the processes in Linux.

The ps Command

The ps, or “process status,” is the most common utility to list processes in the terminal:

The -e option guides ps to show every process regardless of whether the user owns those processes. Furthermore, you can customize the ps command to produce additional details using the “aux” options:

The top Command

If you desire to view the real-time list of system processes, please use the top command. It continuously updates the process list according to new and completed processes, providing more accurate results:

The above command on execution shows the list of processes as per their CPU consumption. Moreover, You can not interact with the terminal until you press “q” to quit the top utility.

The pstree Command

The pstree is very different from the above two commands because it displays the hierarchical relationship of processes in a tree-like structure. It helps you visually understand how a process starts and its connection with other active processes.

The Glances Tool

The Glances tool provides a brief overview of the currently running process. However, you have to install the tool by running the below command: 

After the successful installation, you can open the Glances by running the following command:

A Quick Summary

Knowing how to list processes can help free up the space and turn off the currently running process. This article covered four ways– the top, ps, pstree, and pgrep commands. You can choose to use any of them according to what suits you best. We recommend you use any commands carefully, or you may get errors.