This post covers the changes, bugfixes, and new features in Linux kernel 5.4.102. The release includes 338 patches totaling approximately 160,715 lines of changed or added source code compared to the 5.4 baseline. You can find the source code in the linux-stable tree, or download the 5.4.102 release package directly. The patch bundle is also…
Linux v0.95a Release Notes This document covers the Linux v0.95a root diskette release from March 17, 1992. It documents the changes between v0.95/0.12 and v0.95a. For context on the base 0.95 release, read RELNOTES-0.95 first — this only covers the delta. Changes to the Root Diskette Shell replacement: bash → ash Bash was replaced with…
The SSH quoting problem When passing quoted strings through SSH, shell quoting rules can cause unexpected behavior. The classic issue: ssh user@host cmd “my string” On the remote host, this executes as: cmd my string Instead of treating “my string” as a single argument, the shell splits it. This happens because quotes are processed by…
Listing Shared Memory Segments Use ipcs to see all IPC resources on your system: ipcs -m This shows System V shared memory segments with details like: SHMID: The segment identifier OWNER: User who created it PERMS: Permissions (octal format) BYTES: Size in bytes NATTCH: Number of processes attached For a more compact view focused on…
Checking if STDERR is redirected in Bash You need to detect whether STDERR (file descriptor 2) is connected to a terminal or redirected to a file or pipe. This is useful for conditional logging, color output, or error handling that depends on the output destination. Using file descriptor tests The primary method is the -t…
Printing to STDOUT and STDERR in Bash Understanding file descriptors is fundamental to shell scripting. By default, your shell has three standard streams: STDOUT (FD 1): Standard output, where commands print results STDERR (FD 2): Standard error, where commands print errors and diagnostics STDIN (FD 0): Standard input, where commands read data Basic Output Print…
Getting the parent process ID in C/C++ To retrieve the parent process ID (PPID) of the current running process, use the getppid() system call. This is the standard and portable approach on Unix-like systems including Linux. #include <stdio.h> #include <unistd.h> int main() { pid_t ppid = getppid(); printf(“Parent process ID: %d\n”, ppid); return 0; }…
Getting your process ID Every running process gets a unique identifier from the operating system called a PID (Process ID). You’ll need this when managing processes, logging, creating lock files, or coordinating between parent and child processes. The POSIX standard approach The simplest way is getpid() from unistd.h: #include <unistd.h> #include <stdio.h> int main() {…
Getting the Next Character in ASCII Table with Bash Sometimes you need to find the ASCII character that comes after a given character. This is useful for generating sequences, creating substitution ciphers, or manipulating character ranges in shell scripts. Using printf with ASCII Values The most portable and straightforward approach uses printf to convert between…
Extracting and Removing Trailing Numbers from Strings Extracting or removing trailing numbers from strings is a common task in shell scripting. Whether you’re parsing log files, processing configuration values, or cleaning up filenames, you’ll need reliable methods to handle these operations. Using Parameter Expansion The cleanest approach uses bash parameter expansion, which doesn’t require external…
Getting the Hostname in C Programs on Linux The gethostname() function is the standard POSIX way to retrieve the system’s hostname. It’s straightforward to use and works across Unix-like systems. Basic Implementation #include <unistd.h> #include <stdio.h> int main() { char hostname[256]; if (gethostname(hostname, sizeof(hostname)) == 0) { printf(“Hostname: %s\n”, hostname); } else { perror(“gethostname”); return…
Getting Hostname in Bash in Linux Retrieving the hostname of the machine running your script is essential for logging, node identification in distributed systems, monitoring, and conditional logic based on where code executes. Bash offers multiple approaches with different tradeoffs. Using the $HOSTNAME Variable The quickest method is the $HOSTNAME environment variable, which Bash sets…
Getting Epoch Timestamp in C The epoch timestamp (seconds since January 1, 1970 UTC) is fundamental for Unix timekeeping. Every process needs reliable time access — whether for logging, scheduling, or benchmarking. Basic Second-Level Precision For simple timestamp needs, use time(): #include <time.h> time_t now = time(NULL); printf(“Current epoch: %ld\n”, (long)now); This returns seconds since…
Allowing Root Access to NFS Directories NFS squashes root access to an anonymous user (typically nobody) by default as a security measure. When a client connects as root, the server remaps that user to an unprivileged account, preventing root from having unrestricted access to exported shares. This can cause permission issues if your application genuinely…
Matching tabs with grep Grep handles tab characters in a few different ways depending on your needs. Here’s what actually works. Using \t with extended regex The most straightforward approach uses grep’s extended regular expressions (-E flag): grep -E ‘\t’ filename.txt This matches any line containing a literal tab character. The \t escape sequence is…
Getting the script’s own path in a sourced Bash script When you source a script using . script.sh or source script.sh, the $0 variable doesn’t point to the sourced script—it stays as the path of the parent shell or calling script. This creates a problem if you need the sourced script to know its own…
On my system: $ ulimit -n 1024 Some tools like GATK are aggressive in creating temporary files by creating more than 1000 files under /tmp/. This will cause the program to fail. How to increase the number of files allowed to be opened on Linux? To increase the max number of open files to 10240,…
How to get the directory path and file name from a absolute path in C on Linux? For example, with “/foo/bar/baz.txt”, it will produce: “/foo/bar/” and “baz.txt”. You can use the APIs basename and dirname to parse the file name and directory name. A piece of C code: #include <libgen.h> #include <string.h> char* local_file =…
Setting Environment Variables in csh Use setenv to set an environment variable in csh: setenv VARIABLE value Replace VARIABLE with the name of the variable and value with its value. The variable is immediately available in the current shell and inherited by child processes. Examples Set a simple variable: setenv PATH /usr/local/bin:$PATH setenv EDITOR vim…
Setting and Getting Environment Variables in C on Linux Working with environment variables in C is straightforward using POSIX APIs. The two primary functions are getenv() for retrieval and setenv() for modification. Getting Environment Variables Use getenv() to read an environment variable: #include <stdlib.h> #include <stdio.h> int main(void) { const char *path = getenv(“PATH”); if…