1,340 reputation
179
bio website redhardsupra.blogspot.com
location Laurel, MD
age 37
visits member for 5 years, 1 month
seen 1 hour ago

Jun
6
comment Allow SCP but not actual login using SSH
ForceCommand internal-sftp -u 0077 -d /uploaddir can farther harden it, by forcing a umask on an upload directory. In conjunction with 'ChrootDirectory` it creates a very controlled, isolated upload environment. Bonus note: the default dir and the umask must be set in the ForceCommand, not in the Subsystem directive, if you want them to work.
Jul
30
comment What is the maximum length of a wifi access point's SSID?
The question was about length, and length is irrelevant. The fact that it's not a default, especially in WPA where SSID is used as a salt, it needs to be as random as possible, so in that sense, changing it to something non-default is a good thing.
May
23
comment Best way to go about changing a root password on 3000+ Solaris, AIX, and Linux servers?
Please do not put cleartext passwords on commandline, as it gets logged in shell history. Or set the shell history to /dev/null before you do it.
Jan
7
comment Very slow write performance on Debian 6.0 (AMD64) with DMCRYPT/LVM/RAID1
How does the write performance change when you mount it without sync?
Dec
20
comment Linux Experts Riddle: Network output of 10MB/s on 10GB/s NIC
When copying files over network pipes, turn off compression, copy a file from a ramdisk to another ramdisk, or something simpler, like stream reading /dev/zero, xfering it, and then dumping it out to /dev/null. When dd'ing, remember to play with block sizes and flags on BOTH sides (especially flags might not be symmetric!). When playing with qperf/iperf/netperf, make sure you're controlling window sizes and TCP congestion algorithms. Watch switch statistics. If not meaningful, connect two boxes directly, see if it changes anything. Install new drivers, especially Intel, both Win and LNX.
Oct
18
comment Is there a tool that can take partition table information and partition another based on it?
parted should do it. it can print out partitions in any unit you want, and then more invocations of parted would recreate it step by step.
Oct
10
comment Putting /etc under source control
etckeeper is awesome. Two gotchas tho: for backup, you end up pushing the repo somewhere remote. Please use key-based SSH for that, so it gets done securely. Also, what you store in /etc can be sensitive (think /etc/shadow or any private keys) so make sure that whereever you push the repo to does not have a 'public' webpage, or is being served out through any other unauthenticated means.
Sep
7
comment Linux software RAID that uses system RAM for write cache
Is it per data disk, or disks total? Since it's RAID5, you got N disks in array, but N-1 of data.
Sep
4
comment ksoftirqd hitting 100% on interface with ixgbe driver
Have you tried the newest drivers from Intel's site? I find them to solve a lot of problems, the drivers that come with distros tend to lag behind quite a bit, which causes issues with newer hardware.
Aug
22
comment How to copy a large LVM volume (14TB) from one server to another?
How does a tar pipe handle open/changing files, in comparison to let's say rsync? 14TB move is obviously not going to be an atomic operation ;)
Aug
2
comment Improving TCP performance over a network with small packet loss
I've had good results with hybla, give that a try.
Jul
19
comment How do I parse a log file for one hour with a simple shell script?
Rotate your logs hourly, run analysis on the individual log, which happen to be hour long.
Jun
25
comment Resize base XenServer 6.0 partition
I figured it wasn't that important, since you're screwing with partitions on it ;) in that case, if you have enough space you can yum install gcc and compile gdisk or parted in Dom0.
Mar
23
comment Grepping through the results of apachectl -S
What you pipe to grep is stdout, are you sure that apachectl -S is dumping to stdout, or stderr? Redirect stderr to stdout, grep on that.
Mar
9
comment Anything Close to an NSA Guide for Securing RHEL 6
I don't think RHEL6 have been approved for anything gov/mil operations yet, so no STIGs or SNACs have been released.
Mar
8
comment Faster MySQL DB pull from remote machine into local machine
Good point on using ssh's internal ability to gzip. However, in the modern times, it's advisable to use things like pbzip2, as it can take advantage of (sometimes significant) number of cores. The traditional bzip2 is rather slow, but pbzip2 on a modern box will amaze you.
Mar
6
comment monitor IO to tmpfs partition?
Running PV adds its own bottlenecks, usually invisible at disk speeds, but they will be significant at RAM speeds. Beware.
Feb
15
comment limit linux background flush (dirty pages)
What's your methodology to arrive at the '15MB for dirty_buffers is optimal' part?
Jan
20
comment 2.5 inch drives versus 3.5 inch drives
I could see the contrary: longer tracks contain more data, thus as long as the file system places clusters similar data, the need for seeking altogether might be lower, even though the duration of the seek itself might be longer. From some benchmarks I've seen, seeking just one track takes miliseconds, and it's not that much smaller than seeking a full inside-to-out distance. So I'd rather have denser media, or longer tracks (or whatever allows me to do a sequential read without seeking), than lots of 'fast' seeks. I guess what I'm trying to say is there is no better seek than no seek at all.
Dec
9
comment Setting MTU Per Destination Host
Dunno about OSX, but in normal *nixes, MTU tends to be set per interface, not per host. Maybe you could create a bunch of virtual interfaces with individual MTU's, and give them IP's on different networks, so routing would take care of picking the right interface, and the different MTU in the process? Just an idea... don't shoot me.