How To Use SSHFS to Mount Remote File Systems Over SSH

One of the most effective tools for locating files and directories according to a number of criteria is the Linux find command. Learning how to use this tool can save a lot of time and effort, whether you're a system administrator resolving file system problems or a casual Linux user attempting to search for lost files. You will learn all about find in this tutorial, from its fundamental syntax to its extensive application cases. By the end, you'll be able to use this tool effectively and confidently. Why Use the find Command? Utilizing a number of characteristics, such as permissions, modification date, size, kind, and name, the find program assists you in locating files and folders. It provides unprecedented control and accuracy in contrast to graphical search tools. Here’s what makes it special: Works recursively within directories. Supports complex filtering options. Executes actions on found files (like deleting, moving, or editing them). Handles large datasets efficiently. Let’s dive into its practical applications. Basics of find This is how the general syntax for find looks: find [starting_point] [expression] [starting_point]: The directory where the search starts. Use . to represent the current directory, / for the entire filesystem, or specify a particular path. [expression]: Defines what to search for. This can include file names, types, permissions, sizes, and other attributes. A Simple Example To find a file named notes.txt in your current directory and its subdirectories, run: find . -name "notes.txt" Let’s break this down: .: Search starts within the current directory. -name: Search based on file name. "notes.txt": The target file. Searching by File Name You can search for files using -name or -iname (case-insensitive). Case-Sensitive Search find /home -name "project.txt" Case-Insensitive Search find /home -iname "project.txt" Partial Matches Use wildcards (*) to find files containing specific text: find /var/log -name "*.log" This command locates all .log files in /var/log. Exploring File Types Linux treats everything as a file, but find lets you filter by type using the -type option: Regular Files: -type f Directories: -type d Symbolic Links: -type l Sockets: -type s Character Devices: -type c Block Devices: -type b Example: Finding Directories Only find /etc -type d Filtering by Time Your search can be narrowed down based on when files were accessed, modified, or created. Modified Time (-mtime) Identify which files were changed in the past 7 days: find . -mtime -7 Files modified exactly 7 days ago: find . -mtime 7 Access Time (-atime) Locate files accessed in the last 3 days: find /tmp -atime -3 Change Time (-ctime)  Use -ctime to find files whose metadata changed, such as permissions or ownership. find /var/www -ctime 5 Searching by Size The -size flag allows you to search for files of a specific size. Units of size: k: Kilobytes M: Megabytes G: Gigabytes Exact Size Find files that are 1 MB: find /var -size 1M Greater or Smaller Files Larger than 100MB: find /home -size +100M Smaller than 500KB: find /data -size -500k Combining Conditions Utilize logical operators to combine several search criteria: AND (-a): Default behavior. OR (-o): Specify explicitly. NOT (!): Exclude matches. To find .txt files larger than 1 MB: find . -name "*.txt" -a -size +1M To exclude directories named backup: find /data -type d ! -name "backup" Taking Action on Located Files Find can do more than just search; it can also apply operations on the found files. To do this, use the -exec or -ok flags. Delete Files find /tmp -name "*.tmp" -exec rm {} \; {}: Placeholder for the located file. \;: End of the -exec command. For safer deletion, prompt for confirmation: find /tmp -name "*.tmp" -ok rm {} \; Move or Copy Files find /home/user/docs -name "*.pdf" -exec mv {} /home/user/backup/ \; Run Custom Commands  You can run virtually any command on the located files. For instance, compress all .log files: find /var/log -name "*.log" -exec gzip {} \; Working with Permissions Use these options to search files by ownership or permissions: File Permissions (-perm) Find files with exact permissions: find /etc -perm 644 Locate files writable by others: find /data -perm -o=w User and Group Ownership Files owned by root: find / -user root Files owned by group admin: find / -group admin Avoiding Errors and Boosting Efficiency Ignoring Errors If you lack permissions for certain directories, suppress errors using 2>/dev/null: find / -name "config.yaml" 2>/dev/null Optimizing Searches To improve performance, limit your search depth using -maxdepth: find . -maxdepth 2 -name "*.sh" Use -mindepth to start searching from a certain depth. find . -mindepth 2 -name "*.txt" Real-World Use Cases Housekeeping Logs find /var/log -name "*.log" -mtime +30 -exec rm {} \; Archiving Old Files Move files unused for over a year to an archive directory: find /projects -atime +365 -exec mv {} /archive/ \; Security Audits Find world-writable files, which may pose security risks: find / -perm -o=w Backup Automation Copy all .docx files to a backup directory: find /documents -name "*.docx" -exec cp {} /backup/ \; Combining find with Logical Operators Logical operators such as -and, -or, and -not can be used to build more complex search expressions. These operators allow to search for files that fulfill various conditions concurrently. Find Files with Specific Extensions find . \( -name "*.jpg" -or -name "*.png" \) This searches for files that are either .jpg or .png. Exclude Certain Files find /var/log -type f -not -name "*.gz" This excludes .gz files from the search results. Find Files Modified in the Last Week and Owned by a User find . -mtime -7 -and -user alice Using find for Security Audits The find command can be a valuable tool for identifying security vulnerabilities, such as world-writable files or files with unsafe permissions. Find World-Writable Files find / -type f -perm /o=w This identifies files that are writable by any user. Locate SUID/SGID Files find / -perm /4000 -o -perm /2000 This finds files with the SUID or SGID bit set, which can sometimes pose security risks. Managing Large Data Sets When managing large file systems, searching efficiently is key. Here are a few tips for optimizing find usage: Limit Results with -print and head find /data -type f -name "*.csv" -print | head -n 10 This command quickly previews the first 10 results. Search in Parallel Use find with xargs for parallel processing: find /large_dir -type f -print0 | xargs -0 -P4 -I{} echo "Processing {}" This processes files in parallel using four threads (-P4). Managing Special File Name Characters Files with spaces, newlines, or other special characters in their names can cause issues when using find. To avoid problems, use -print0 with xargs or other commands. Delete Files Containing Special Characters Safely find . -name "*.bak" -print0 | xargs -0 rm Conclusion One useful utility that can revolutionize your Linux system interaction is the find command. It gives you the ability to handle files with accuracy and originality, from basic searches to intricate workflows. You will soon be able to utilize this program to its fullest extent if you practice the instructions provided here and try out various settings. No matter your level of experience as an administrator, find is a crucial tool for your Linux toolbox. You can try our reliable Linux VPS hosting for your projects.

One of the core principles of Unix systems is the extensive use of text data: configuration files, as well as input and output data in *nix systems, are often organized as plain text. Regular expressions are a powerful tool for manipulating text data. This guide delves into the intricacies of using regular expressions in Bash, helping you fully harness the power of the command line and scripts in Linux. What Are Regular Expressions? Regular expressions are specially formatted strings used to search for character patterns in text. They resemble shell wildcards in some ways, but their capabilities are much broader. Many text-processing utilities in Linux and programming languages include a regular expression engine. However, different programs and languages often employ different regular expression dialects. This article focuses on the POSIX standard to which most Linux utilities adhere. The grep Utrequires at least one match of theility The grep program is the primary tool for working with regular expressions. grep reads data from standard input, searches for matches to a specified pattern, and outputs all matching lines. grep is typically pre-installed on most distributions. You can try the commands in a virtual machine or a VPS to practice using regular expressions. The syntax of grep is as follows: grep [options] regular_expression [file...] The simplest use case for grep is finding lines that contain a fixed substring. In the example below, grep outputs all lines that contain the sequence nologin: grep nologin /etc/passwd Output: daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin games:x:5:60:games:/usr/games:/usr/sbin/nologin ... grep has many options, which are detailed in the documentation. Here are some useful options for working with regular expressions: -v — Inverts the match criteria. With this option, grep outputs lines that do not contain matches: ls /bin | grep -v zip# Output:411toppm 7z 7za 7zr ... -i — Ignores case. -o — Outputs only the matches, not the entire lines: ls /bin | grep -o zip# Output:zip zip zip zip ... -w — Searches for lines containing whole words matching the pattern. ls /bin | grep -w zip# Output:gpg-zipzip For comparison, the same command without the -w option also includes lines where the pattern appears as a substring within a word. ls /bin | grep zip# Output:bunzip2 bzip2 bzip2recover funzip Basic Regular Expressions (BRE) As previously mentioned, there are multiple dialects of regular expressions. The POSIX standard defines two main types of implementations: Basic Regular Expressions (BRE), which are supported by almost all POSIX-compliant programs, and Extended Regular Expressions (ERE), which allow for more complex patterns but aren't supported by all utilities. We'll start by exploring the features of BRE. Metacharacters and Literals We've already encountered simple regular expressions. For example, the expression “zip” represents a string with the following criteria: it must contain at least three characters; it includes the characters “z”, “i”, and “p” in that exact order; and there are no other characters in between. Characters that match themselves (like “z”, “i”, and “p”) are called literals. Another category is metacharacters, which are used to define various search criteria. Metacharacters in BRE include: ^ $ . [ ] * \ - To use a metacharacter as a literal, you need to escape it with a backslash (\). Note that some metacharacters have special meanings in the shell, so enclose it in quotes when passing a regular expression as a command argument. Any Character The dot (.) metacharacter matches any character in that position. For example: ls /bin | grep '.zip' Output: bunzip2 bzip2 bzip2recover funzip gpg-zip gunzip gzip mzip p7zip pbzip2 preunzip prezip prezip-bin streamzip unzip unzipsfx One important detail: the zip program itself isn’t included in the output because the dot (.) metacharacter increases the required match length to four characters. Anchors The caret (^) and dollar sign ($) in regular expressions serve as anchors. This means that, when included, a match can only occur at the start of a line (^) or at the end ($). ls /bin | grep '^zip'# Output:zip zipcloak zipdetails zipgrep …ls /bin | grep 'zip$'# Output:funzip gpg-zip gunzip ...ls /bin | grep '^zip$'# Output:zip The regular expression ^$ matches empty lines. Character Sets Besides matching any character in a given position (.), regular expressions allow for matching a character from a specific set. This is done with square brackets. The following example searches for strings matching bzip or gzip: ls /bin | grep '[bg]zip'# Output:bzip2bzip2recovergzip All metacharacters lose their special meaning within square brackets, except two. If a caret (^) is placed immediately after the opening bracket, the characters in the set are treated as excluded from that position. For example: ls /bin | grep '[^bg]zip' Output: bunzip2 funzip gpg-zip gunzip mzip p7zip preunzip prezip prezip-bin streamzip unzip unzipsfx With negation, we get a list of filenames containing zip but preceded by any character other than b or g. Note that zip is not included here; the negation requires the presence of some character in that position. The caret serves as a negation only if it appears immediately after the opening bracket; otherwise, it loses its special meaning. Using a hyphen (-), you can specify character ranges. This lets you match a range of characters or even multiple ranges. For instance, to find all filenames that start with a letter or a number: ls ~ | grep '^[A-Za-z0-9]' Output: backup bin Books Desktop docker Documents Downloads GNS3 ... POSIX Character Classes When using character ranges, one challenge is that ranges can be interpreted differently based on locale settings. For instance, the range [A-Z] may sometimes be interpreted lexicographically, potentially excluding lowercase a. To address this, the POSIX standard provides several classes that represent various character sets. Some of these classes include: [:alnum:] — Alphanumeric characters; equivalent to [A-Za-z0-9] in ASCII. [:alpha:] — Alphabetic characters; equivalent to [A-Za-z] in ASCII. [:digit:] — Digits from 0 to 9. [:lower:] and [:upper:] — Lowercase and uppercase letters, respectively. [:space:] — Whitespace characters, including space, tab, carriage return, newline, vertical tab, and form feed. Character classes don’t provide an easy way to express partial ranges, like [A-M]. Here’s an example of using a character class: ls ~ | grep '[[:upper:]].*' Output: Books Desktop Documents Downloads GNS3 GOG Games Learning Music ... Extended Regular Expressions (ERE) Most POSIX-compliant applications and those using BRE (such as grep and the stream editor sed) support the features discussed above. The POSIX ERE standard allows for more expressive regular expressions, though not all programs support it. The egrep program traditionally supported the ERE dialect, but the GNU version of grep also supports ERE when run with the -E option. In ERE, the set of metacharacters is expanded to include: ( ) { } ? + | Alternation Alternation allows for a match with one of multiple expressions. Similar to square brackets that allow a character to match one of several characters, alternation allows for matching one of multiple strings or regular expressions. Alternation is represented by the pipe (|): echo "AAA" | grep -E 'AAA|BBB'# Output:AAA echo "BBB" | grep -E 'AAA|BBB'# Output:BBB echo "CCC" | grep -E 'AAA|BBB'# Output: (no match) Grouping You can group elements of regular expressions and treat them as a single unit using parentheses. The following expression matches filenames starting with bz, gz, or zip. Without the parentheses, the regular expression would change meaning to match filenames starting with bz or containing gz or zip. ls /bin | grep -E '^(bz|gz|zip)' Output: bzcat bzgrep bzip2 bzip2recover bzless bzmore gzexe gzip zip zipdetails zipgrep zipinfo zipsplit Quantifiers Quantifiers specify the number of times an element can occur. BRE supports several quantifiers: ? — Matches the preceding element zero or one time, meaning the previous element is optional: echo "tet" | grep -E 'tes?t'# Output:tet echo "test" | grep -E 'tes?t'# Output:test echo "tesst" | grep -E 'tes?t'# Output: (no match) * — Matches the preceding element zero or more times. Unlike ?, this element can appear any number of times: echo "tet" | grep -E 'tes*t'# Output:tet echo "test" | grep -E 'tes*t'# Output:test echo "tesst" | grep -E 'tes*t'# Output:tesst + — Similar to *, but requires at least one match of the preceding element: echo "tet" | grep -E 'tes+t'# Output: (no match) echo "test" | grep -E 'tes+t'# Output:test echo "tesst" | grep -E 'tes+t'# Output:tesst In BRE, special metacharacters { and } allow you to specify minimum and maximum match counts for the preceding element in four possible ways: {n} — Matches if the preceding element occurs exactly n times. {n,m} — Matches if the preceding element occurs at least n and at most m times. {n,} — Matches if the preceding element occurs n or more times. {,m} — Matches if the preceding element occurs no more than m times. Example: echo "tet" | grep -E "tes{1,3}t"# Output: (no match) echo "test" | grep -E "tes{1,3}t"# Output:test echo "tesst" | grep -E "tes{1,3}t"# Output:tesst echo "tessst" | grep -E "tes{1,3}t"# Output:tessst echo "tesssst" | grep -E "tes{1,3}t"# Output: (no match) Only the lines where s appears one, two, or three times match the pattern. Regular Expressions in Practice To conclude, let’s look at a couple of practical examples of how regular expressions can be applied. Validating Phone Numbers Suppose we have a list of phone numbers where the correct format is (nnn) nnn-nnnn. Out of a list of 10 numbers, three are incorrectly formatted. cat phonenumbers.txt Output: (185) 136-1035 (95) 213-1874 (37) 207-2639 (285) 227-1602 (275) 298-1043 (107) 204-2197 (799) 240-1839 (218) 750-7390 (114) 776-2276 (7012) 219-3089 The task is to identify the incorrect numbers. We can use the following command: grep -Ev '^\([0-9]{3}\) [0-9]{3}-[0-9]{4}$' phonenumbers.txt Output: (95) 213-1874(37) 207-2639(7012) 219-3089 Here, we used the -v option to invert the match and output only lines that do not match the specified format. Since parentheses are considered metacharacters in ERE, we escaped them with backslashes to treat them as literals. Finding Improper File Names The find command supports checking paths with regular expressions. It’s important to note that, unlike grep which matches parts of lines, find requires the whole path to match. Suppose we want to identify files and directories containing spaces or potentially problematic characters. find . -regex '.*[^-_./0-9a-zA-Z].*' The .* sequences at the beginning and end represent any number of any characters, which is necessary because find expects the entire path to match. Inside the square brackets, we use negation to exclude valid filename characters, meaning any file or directory name containing characters other than hyphens, underscores, digits, or Latin letters will appear in the output. Conclusion This article has covered a few practical examples of Bash regular expressions. Creating complex regular expressions might seem challenging at first. But over time, you’ll gain experience and skill in using regular expressions for searches across various applications that support them.

DNF (Dandified Yum) is the next-generation version of Yum, the default package manager for CentOS and Fedora distributions. It is designed to resolve dependencies more efficiently, handle larger package sets, and improve performance over its predecessor. DNF simplifies the management of software packages by allowing users to install, update, and remove packages from the command line with a user-friendly interface. Installing and Removing Packages with DNF One of the primary functions of DNF is installing and removing software packages. To install a package using DNF, you need root or sudo privileges. The syntax is straightforward: sudo dnf install package_name For example, to install the Apache HTTP server: sudo dnf install httpd To remove a package, the command is similar: sudo dnf remove package_name For example, to remove Apache HTTP server: sudo dnf remove httpd Updating and Upgrading Packages Keeping your system up to date is essential for security and performance. DNF makes this process simple. To update all the packages on your system, use: sudo dnf update This command will update installed packages to the latest versions available in the configured repositories. If you want to upgrade your entire system to the latest release (such as when moving between CentOS versions), you can use: sudo dnf upgrade The difference between update and upgrade is that the latter will also remove obsolete packages, whereas update does not. Searching for Packages in DNF DNF allows users to search for packages before installing them. This is helpful if you're unsure of the exact package name or want to explore available options. To search for a package: sudo dnf search <keyword> For example, to search for packages related to Apache: sudo dnf search apache DNF will list all packages that match the search term, along with a brief description. Managing Repositories with DNF Repositories are essential for managing where DNF pulls its packages from. DNF automatically handles repository configuration files, usually located in /etc/yum.repos.d/. You can add, enable, or disable repositories with DNF. To add a new repository, you need to create a .repo file in /etc/yum.repos.d/. For example, let's say you want to add the EPEL (Extra Packages for Enterprise Linux) repository, which provides additional packages not available in the default CentOS repositories. Install the EPEL repository using DNF EPEL is available as a package that can be installed directly: sudo dnf install epel-release This command automatically creates the necessary .repo file and enables the EPEL repository. Manually adding a repository If you want to manually add a repository, you would create a .repo file, for instance, myrepo.repo, in /etc/yum.repos.d/, and add the following content: [myrepo]name=My Custom Repobaseurl=http://example.com/repo/centos/$releasever/$basearch/enabled=1gpgcheck=1gpgkey=http://example.com/repo/RPM-GPG-KEY-myrepo Here: name specifies the name of the repository. baseurl defines the URL from where the packages will be downloaded. enabled=1 ensures the repository is active. gpgcheck=1 enables GPG key checking for security. gpgkey provides the URL to the GPG key used to verify the packages. To disable the epel repository: sudo dnf config-manager --set-enabled epel To enable it again: sudo dnf config-manager --set-enabled epel Cleaning Up Unused Packages Over time, your system may accumulate unnecessary packages and cache files, which take up valuable space. DNF includes a built-in command to clean up unused packages and free up disk space: sudo dnf autoremove This will remove any orphaned packages that are no longer required by the system. Additionally, you can clean up cached data using: sudo dnf clean all This command clears all cached package files stored in /var/cache/dnf/. Troubleshooting DNF Issues Occasionally, you may encounter issues when managing packages with DNF. Common problems include broken dependencies or repository errors. Here are some troubleshooting tips: Broken dependencies: If you're facing dependency issues, try running: sudo dnf install --best --allowerasing This command attempts to resolve conflicts by allowing DNF to erase conflicting packages. Corrupted cache: If the cache becomes corrupted, clean it up using: sudo dnf clean metadata Failed transactions: If a DNF transaction fails, try rebuilding the database: sudo rpm --rebuilddb By using these tips, you can quickly resolve most issues you might face with DNF. Conclusion DNF is a powerful and efficient package manager that makes software management on CentOS easy. From installing and updating packages to managing repositories and cleaning up unused files, DNF provides a wide range of features to ensure your system runs smoothly. With this guide, you should be well-equipped to handle package management tasks on your CentOS system. On Hostman, you can try Linux VPS hosting for your projects.