readlink -m can get canonical file name by resolving every symlinks in every component of the given path recursively. In Python, the os.readlink() function does not do so. Any equivalent function in Python to the readlink -m command line? Specifically, it does: canonicalize by following every symlink in every component of the given name recursively,…
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 history commands very effectively in bash shell command line? Just enter CTRL+r The function of above is: (reverse-i-search)`’: It is very fast and efficient.
# ssh root@192.168.122.96 root@192.168.122.96’s password: Permission denied, please try again. Do according to [1]. NOTE: on Ubuntu, remember to restart ssh service like this “sudo restart ssh”. [1] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/v2v_guide/preparation_before_the_p2v_migration-enable_root_login_over_ssh
Evolution’s default Email sort order is not very convenient, at least to me. How to apply the settings of sort order for a folder to all folders in Evolution? Manually setting the email sort order for each dir is tedious. Evolution has a function to “apply the same view settings to all folder” so that…
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 14.04 Trusty > sudo apt-get install dmidecode > sudo dmidecode -s system-serial-number I tried this on several Linux boxes with CentOS 7 and it seems A physical node returns a string like System Serial Number. A KVM VM returns a string like 3fd12bba-12d4-48c7-875a-7a5f57ed8a9a….
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…
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…
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 CentOS 7 to convert .deb to .rpm? alien is already in EPEL and it makes it quite easy to install it in CentOS 7. First, enable EPEL following this tutorials. Then, install alien by # yum install alien Then alien should be ready: # yum info alien Installed…