Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Save a file in vim without the needed permissions
Answer:
Very often, you opened a file using vim, edited it and find out that the file is opened as read only, i.e. you don't have permission to make any change(s).
What will you do? Simplest method is to save it into a temp file and rename it afterward.
However, there exist a simple method that allow you to save the file anyway.
Instead of using :wq, you enter the following.
:w !sudo tee %
That is what you need.
Check what Linux kernel modules are loaded
Answer:
To find out what Linux kernel modules are loaded:
# lsmod
Module Size Used by
ipt_REJECT 3584 1
ipt_LOG 6404 1
xt_limit 3236 2
xt_tcpudp 3616 10
xt_state 2432 6
ipt_addrtype 2912 4
ip6_tables 22576 0
nf_nat_irc 2688 0
nf_conntrack_irc 6552 1 nf_nat_irc
nf_nat_ftp 3584 0
nf_nat 22164 2 nf_nat_irc,nf_nat_ftp
nf_conntrack_ipv4 16376 8 nf_nat
nf_defrag_ipv4 2400 1 nf_conntrack_ipv4
nf_conntrack_ftp 9016 1 nf_nat_ftp
...
To find out more information for a specific module
# modinfo ip6_tables
filename: /lib/modules/2.6.31-14-server/kernel/net/ipv6/netfilter/ip6_tables.ko
description: IPv6 packet filter
author: Netfilter Core Team
license: GPL
srcversion: 17E938A990111BB4A2F854B
depends: x_tables
vermagic: 2.6.31-14-server SMP mod_unload modversions
How to execute prorgam in the current directory
Answer:
1. Make sure the program is executable
# chmod a+x my_program
2. Run it by appending ./ in the front of file name
# ./my_program
./ is needed if the current directory is not in your current search path (PATH)
How many worker_processes should I use in Nginx?
Answer:
In the Nginx configuration (nginx.conf), the default worker_processes is 1.
e.g.
worker_processes 1;
However, as nowadays most servers are multi-core/multi-processor machine, it is a waste to only use 1 worker process.
The recommended worker_processes is equal to the number of CPU cores, e.g. if you have a dual Quad Core server, you should set to 8.
worker_processes 8;
Speedup sed search and replace
Answer:
If you have a very large file, sometimes you can speed up sed by using the following method:
Original method:
# sed 's/foo/bar/g' filename
Optimized method:
# sed '/foo/ s/foo/bar/g' filename
The second method is faster since substitution is only performed when the search string is found.
