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Tag: linux

Printf tab character as hex

In a restricted shell i have only access to execute printf (no awk, hexdump, xxd, …), so i used this script to print a file as hex: issue: last line (printf %02x ‘${a:$i:1}) does not work for some character like s,r,n,t,… i handle space character with (printf “%X” ‘ ‘…

RDMA – how does the ibv_post_send know the CQ?

I’m trying to learn RDMA. My question is, when doing ibv_post_send, I should get a completion event on a completion queue. But how does the ibv_post_send know to which completion queue? From what I see here, I could have created many. Answer Turns out when initiating a QP, it can be assigned to a send C…

Simulate permissions for non-login user

I want to perform some actions on behalf of some non-login users, such as e.g. www-data or uwsgi. My purpose is to test some permissions, check what dirs they can modify etc etc. Is there a recommended way of going about this, other than creating a shell and password for them and su ? edit: When I try to su

Ending a Loop with EOF (without enter)

i am currently trying to end a while loop with something like this: } When i press CTRL+D on my Ubuntu, it ends the loop immediately. But on Windows i have to press CTRL+Z and then press ENTER to close the loop. Can i get rid of the ENTER on Windows? Answer The getchar behavior For linux the EOF char

Curl/sed command not processing inputs correctly

I’m having some trouble with getting this to do what I want it to do. So basically what I want is to use curl to get a .txt file from a url, then sort through it to find the word specified by the user input. Then mark all those words with a * and put them in a file specified

Editing single value in file in C efficiently

I have a C program that currently edits a single value in a parameter file by using sed through a system call. I’d like to change the program to use the C file libraries to edit this value, but the only way I know how to do this is by reading in the entire file, changing the value, and rewriting

What type of memory objects does `shm_open` use?

Usually, shared memory is implemented using portions of On-Disk files mapped to processes address spaces. Whenever a memory access occurs on the shared region, the filesystem is involved to write changes on the disk which is a great overhead. Typically, a call to fopen() returns a file descriptor which is pas…