How to Get the Canonical File Name in Python (readlink -m) The Linux command readlink -m resolves a path to its absolute, canonical form, following all symlinks and resolving .. or . components. In Python, we have a direct equivalent. The Python Equivalent: os.path.realpath() import os canonical_path = os.path.realpath(“./../folder/./file.txt”) The Modern pathlib Way from pathlib…
How to list start and end of a partition by the sectors in parted on Linux? The default behavior seems be listing the start and end by bytes in parted. # parted /dev/sdc print Model: Innostor IS888 ext. HDD (scsi) Disk /dev/sdc: 2000GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End…
How to Search Bash History Effectively The “Up Arrow” is slow. In 2026, every power user relies on incremental history search to recall complex commands from the past. The Magic Shortcut: Ctrl + R Press Ctrl + R. Start typing a keyword from the command you remember (e.g., “docker”). Bash will show the most recent…
Why You Can’t Login to a Remote Server as Root (and How to Fix It) If you’ve tried ssh root@my-server and got a “Permission denied” error, it’s not a bug—it’s a security feature. The Reason: PermitRootLogin In the /etc/ssh/sshd_config file, the line PermitRootLogin is set to prohibit-password or no by default on almost all modern…
How to Apply Email Sort Order to All Folders in Evolution By default, Evolution remembers the sort order (e.g., by Date, Sender, or Subject) for each folder individually. If you want a consistent view across your entire mailbox, you have to set it globally. The Steps Open Evolution and go to Edit -> Preferences. Select…
How to iterate all dirs and files in a dir in C++? To open a dir, we can use opendir() to open a directory stream. DIR *opendir(const char *name); Then we can use readdir() to iterate the directory stream. struct dirent *readdir(DIR *dirp); Here is an example C++ program using these 2 library functions. #include…
How to remove newline characters from a string in C++? For example, a string like line 1 line 3 line 4 should be converted to line 1line 3line 4 Method 1: use `erase()` and `remove()` In short, use this code snippet: input.erase(std::remove(input.begin(), input.end(), ‘\n’), input.end()); std::remove() shifts all elements that are equal to the value…
How to get a path’s mtime in C++ on Linux? The path can be a file or a dir. You may call the standard library function lstat() for the file or dir under the path. int lstat(const char *pathname, struct stat *statbuf); From the returned stat struct, there is a field st_mtim which is the…
How to test whether a given path is a directory or a file in C++? For example, pathtype(“/”) –> “a dir” pathtype(“/tmp/file.txt”) –> “a file” # if there is a file file.txt pathtype(“/tmp/dir.txt”) –> “a dir” # if there is a dir named dir.txt The type of a file/dir can be found out using lstat()…
How to cat a single file’s content from a tar without unpacking it on Linux? For example, I know there is a file README.txt in a tar tools.tar.gz . How to cat the content of README.txt out? You can do this by using a combination of tar‘s options and arguments. -O, –to-stdout Extract files to…
how to list and delete shared memory in linux? List all shared memories in your Linux Systems > $ ipcs -m Delete specific one > $ ipcrm -M 0x0001869c
If we want to check one program on one remote server, we need to know this server’s IP and port number. How to get this program’s port number in the remote server? # netstat -tulpn Remember to run this program with root permission since some programs can only be accessed by root.
How to get a server’s serial number remotely? Tested on Linux Ubuntu 24.04 LTS Trusty > sudo apt-get install dmidecode > sudo dmidecode -s system-serial-number I tried this on several Linux boxes with Rocky Linux 9 and it seems A physical node returns a string like System Serial Number. A KVM VM returns a string…
Login without PWD is fast and efficient. Running commands in server from local machine also have these benefits. login without PWD: add PC A’s public key to PC B’s authorized keys. > a@A:~> cat .ssh/id_rsa.pub | ssh b@B ‘cat >> .ssh/authorized_keys’ > b@B’s password: Run command remotely ssh root@MachineB “ls” NOTE: running commands remotely is…
Within a Bash script, how to judge whether its STDERR is redirected to a file in Bash on Linux? For example, ./script.sh /tmp/log 2>&1 Can script.sh detect that its STDERR is redirected? Knowing the destination file is better. To test whether a script’s STDERR (or STDOUT) is redirected to a file, check by [[ -f…
diff on Linux is a very handy tool. Any good diff alternatives on Windows to find differences between 2 files? A GUI program will be better on Windows. I would recommend meld for Windows users. Meld is a visual diff and merge tool open source software. meld is available on Linux, Windows and Mac OS…
how to set linux date and time in commands For example, to change date to 14 Nov 2017 11:57:00, the command would be, $ sudo date –set “14 Nov 2017 11:57:00” Tue Nov 14 11:57:00 HKT 2017
What is the difference between work conserving I/O scheduler and non-work conserving I/O scheduler? In a work-conserving mode, the scheduler must choose one of the pending requests, if any, to dispatch, even if the pending requests are far away from the current disk head position. The rationale for non-work-conserving schedulers, such as the anticipatory scheduler…
In Python, os.makedirs() with 0777 mode can not give others write permission The code is as follows $ python Python 2.7.5 (default, Aug 4 2017, 00:39:18) [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux2 Type “help”, “copyright”, “credits” or “license” for more information. >>> import os >>> os.makedirs(“/tmp/test1/test2”, 0777) >>> The created dirs are not…
How to install the alien command on Rocky Linux 9 to convert .deb to .rpm? alien is already in EPEL and it makes it quite easy to install it in Rocky Linux 9. First, enable EPEL following this tutorials. Then, install alien by # yum install alien Then alien should be ready: # yum info…