Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
How do I find and replace non-printable characters in vim?
Answer:
To replace non-printable characters in vim, e.g. get rid of ^M, you need to use the following replace method.
:%s/^M//g
Notes: The ^M above was inputted by holding down "Ctrl+v+m" at the same time.
Send ARP REQUEST to a neighbour host in Linux
Answer:
The arping command allow you to Ping destination on device interface by ARP packets, using source address source.
E.g.
# arping -U 192.168.1.5
The above command send an Unsolicited ARP request to update neighbours' ARP caches.
What are the differences between Mutex and Semaphore?
Answer:
A very good example was given in the Wikipedia
Mutex:
Is a key to a toilet. One person can have the key - occupy the toilet - at the time. When finished,
the person gives (frees) the key to the next person in the queue.Semaphore:
Is the number of free identical toilet keys. Example, say we have four toilets with identical locks
and keys. The semaphore count - the count of keys - is set to 4 at beginning (all four toilets are free),
then the count value is decremented as people are coming in. If all toilets are full, ie. there are no
free keys left, the semaphore count is 0. Now, when eq. one person leaves the toilet, semaphore is
increased to 1 (one free key), and given to the next person in the queue.So, A mutex is really a semaphore with value 1
How to clear cache from memory in Linux?
Answer:
From time to time, you might observed memory in Linux aren't free'ed after used, and they can be shown in the cached column of the free command.
# free -m
total used free shared buffers cached
Mem: 1033 468 564 0 0 343
-/+ buffers/cache: 124 908
Swap: 255 1 254
To manually free it, try
# sync; echo 3 > /proc/sys/vm/drop_cachesAnd try the free command again.
# free -m
total used free shared buffers cached
Mem: 1033 135 897 0 0 10
-/+ buffers/cache: 124 908
Swap: 255 1 254
Update the local CVS repository
Answer:
To update the local working CVS repository, you can use the command:
# cvs update -P
The -P flag is useful as it prune empty directories.
