Basics
error: stat of /var/log/cron failed: No such file or directory
by dino on Jul.29, 2008, under Basics, Command Line, Uncategorized, Virtuozzo, WebMin
Hi guys… Today I faced a issue with a new VPS installed with EZ template Centos 5.2. I was preparing the VPS with logwatch, apf and other security and got cron error under roots mail.
Cron errors shows log errors :
/etc/cron.daily/logrotate:
error: stat of /var/log/boot.log failed: No such file or directory
error: stat of /var/log/cron failed: No such file or directory
OR
You do not find log files updating
This was due to the syslog daemon not running. Check if the service is running and restart. Your server may have syslogd daemon on rsyslogd depending on your OS.
I had rsyslogd on Centos 5.2
# /etc/init.d/rsyslog status
rsyslogd is stopped
rklogd is stopped# /etc/init.d/rsyslog start
Starting system logger: [ OK ]
Starting kernel logger: [ OK ]
Check if the service is being started at the starup :
# chkconfig –list | grep rsyslog
rsyslog 0:off 1:off 2:off 3:off 4:off 5:off 6:off
Use Command to enable the daemon at startup
# chkconfig rsyslog on
The log files were not being created due to the daemons stopped, after restart all started generating.
Cheers!
cPanel / APF – Passive FTP issue
by dino on Jul.11, 2008, under Basics, Uncategorized
The following web site will redirect you to a very well written article, which will cover the basics of “Passive vs Active” mode functions.
Active FTP vs. Passive FTP, a Definitive Explanation
After FTP connection has been made, The FTP server will generally choose a random port within a certain range to use and tell the client to connect to, but when the firewall is setup to block this port, the connection can not be made and the client times out. Error example below :
[14:55:16] PASV
[14:55:16] 227 Entering Passive Mode (74,86,43,171,13,209)
[14:55:16] Opening data connection to 74.86.43.171 Port: 3537
[14:55:16] LIST -aL
[14:55:37] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
Opening the ports on APF
The first step was to tell APF to have a range of ports open for passive FTP connections. You can put in any range you want as long as it doesn’t conflict with another service. For this we’re going to use the range of 35000-35500.
Will be using vi in this How-To. Please see the Basic Guide to Vim
cd /etc/apf; vi conf.apf
Find IG_UDP_CPORTS and add passive ports 35000-35500 to look like :
IG_TCP_CPORTS=”20,21,22,25,26,53,80,110,143,161,443,465,623,993,995,2082,2083,2086
,2087,2095,2096,3306,3389,6666,35000_35500“
Save the file and restart APF with
/etc/init.d/apf restart
Setting up the FTP Server (Pure-FTPD):
Now you need to tell PureFTPd to use those ports for passive connections. Open up the file /etc/pure-ftpd.conf in your editor and look for the following.
# PassivePortRange 30000 50000
Two things to note. One, the setting is commented out and two the range doesn’t match what we opened in APF. So change it to the following.
PassivePortRange 35000 35500
Restart the PureFTP server with
/etc/init.d/pure-ftpd restart
Test the connections and your are done !
Linux Memory Management
by dino on Jul.05, 2008, under Basics
Scenario: Customer is concerned that only 100MB of their 2GB of memory is as unused or free when running the free command. However, no processes appear to be consuming large amounts of memory, and the server is not running slow.
Cause: This is not a problem, but rather a result of the way linux manages its memory. On boot linux will typically display a large amount of free memory, as no processes have started to address it yet. Once processes run, Linux will cache that memory so it is quickly addressed for the next session. What this means is that on *most* linux distros, you’ll notice that a very small amount of memory is free, even though the machine is having no problems processing data (unlike, for instance a Windows server that would be quite slow with 150K of “free” memory). The best way to judge if the server is running low on memory, is if the swap space is being addressed. If the swap is occasionally hit, using a very small amount of memory, there is no cause for concern as that space will still be addressed. However, if a large amount of swap space is being used (50% or more) then the client may want to consider a memory upgrade.
Basically, the free memory isn’t the amount of memory that is not doing something, it’s the sum total of LowMem and HiMem that he kernel has left to address.
Performance tuning tools: ps, top, sar, iostat, and vmstat
by dino on Jun.02, 2008, under Basics
Performance tuning tools :by Matt Frye
- P.S.—I want to see my processes
- Being on top
- Sar, yes, sar!
- Check your system, STAT!
- About the author
As a system administrator, part of your daily duties is to monitor systems for performance and to tune systems where necessary. While there are expensive software products and benchmarking tools that can hone a machine to optimum efficiency, there exist several basic tools within Linux® that permit the knowledgeable system administrator to gather information and use the valuable information to make decisions about where and when to tune a system.
P.S.—I want to see my processes
One of the most basic tools we can use is the utility ps. ps provides a snapshot of current processes. This snapshot can range from myself as a single user (such as what active processes I have running) to all the processes on the system. The simple example of course is to run the ps command with no options, which produces output similar to:
PID TTY TIME CMD 2873 pts/1 00:00:00 bash 3002 pts/1 00:00:00 ps
Example 1. Basic output of ps
We see in Example 1, “Basic output of ps” that we get some minimal information about the processes we are running, including ps itself. ps displays the process ID (PID), the terminal associated with the process (TTY), the cumulated CPU time in [dd-]hh:mm:ss format (TIME), and the executable name (CMD). Spectacular, right? Well, ps does this and a whole lot more. I should mention at this point that the version of ps that I am using for this article is something special compared to the ps of yester-year and of your classic UNIX®. This ps, procps version 3.2.5, accepts several kinds of options: UNIX options, which may be grouped and must be preceded by a dash, BSD options, which may be grouped and must not be used with a dash, and GNU long options, which are preceded by two dashes. For the uninitiated, those who are new to Linux, or refugees from some older BSD or System V variant, this is good news. A system administrator can track down a process via several sets of options.
root 2784 2774 0 22:45 pts/2 00:00:00 su - mfrye mfrye 2785 2784 0 22:45 pts/2 00:00:00 -bash root 2895 1870 0 23:04 ? 00:00:00 sshd: mfrye [priv] mfrye 2897 2895 0 23:04 ? 00:00:00 sshd: mfrye@pts/3 mfrye 2898 2897 0 23:04 pts/3 00:00:00 -bash mfrye 3274 2785 0 23:34 pts/2 00:00:00 ps -ef mfrye 3275 2785 0 23:34 pts/2 00:00:00 grep mfrye
Example 2. Output of ps -ef | grep mfrye
root 2784 0.0 0.0 71368 1288 pts/2 S 22:45 0:00 su - mfrye mfrye 2785 0.0 0.0 55124 1536 pts/2 S 22:45 0:00 -bash root 2895 0.0 0.1 38228 2660 ? Ss 23:04 0:00 sshd: mfrye [priv] mfrye 2897 0.0 0.1 38228 2748 ? S 23:04 0:00 sshd: mfrye@pts/3 mfrye 2898 0.0 0.0 55124 1528 pts/3 Ss 23:04 0:00 -bash mfrye 3272 0.0 0.0 52948 872 pts/2 R+ 23:34 0:00 ps aux mfrye 3273 0.0 0.0 51192 636 pts/2 S+ 23:34 0:00 grep mfrye
Example 3. Output of ps -aux | grep mfrye
In Example 2, “Output of ps -ef | grep mfrye” and Example 3, “Output of ps -aux | grep mfrye”, we see the output of ps with different arguments. We can use this output to track a particular set of processes (owned by mfrye) via either of two sets of options (UNIX & BSD, respectively). So what’s the big deal, you’re thinking? OK, so bash is a pretty tame example. In cases where another process, perhaps one that consumes more memory, or some other resource, than you want, ps can be a very quick, easy, and effective way to track that process down. So now we’ve tracked down a particular process, but we don’t know much more than some basic information about the process’s CPU usage in terms of accumulated CPU time, which as you may appreciate, is not ideal. Luckily, there’s more.
Being on top
To track a process in relation to the system usage, another basic performance monitoring tool is top. To start top, simply run top from the command line. A typical glimpse of top output without any formatting can be seen in Example 4, “Basic output of top”.
top - 23:50:16 up 3:25, 1 user, load average: 0.00, 0.00, 0.00
Tasks: 88 total, 1 running, 87 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0% us, 0.0% sy, 0.0% ni, 100.0% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 2055112k total, 227684k used, 1827428k free, 53556k buffers
Swap: 2096472k total, 0k used, 2096472k free, 100884k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 16 0 4876 596 500 S 0.0 0.0 0:00.78 init
2 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
3 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
4 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/1
5 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/1
6 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/2
7 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/2
8 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/3
9 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/3
10 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/0
11 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/1
12 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/2
13 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 events/3
14 root 19 -5 0 0 0 S 0.0 0.0 0:00.00 khelper
15 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kthread
22 root 20 -5 0 0 0 S 0.0 0.0 0:00.00 kacpid
106 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/0
107 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/1
108 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/2
109 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 kblockd/3
112 root 15 0 0 0 0 S 0.0 0.0 0:00.00 khubd
162 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pdflush
163 root 15 0 0 0 0 S 0.0 0.0 0:00.01 pdflush
166 root 13 -5 0 0 0 S 0.0 0.0 0:00.00 aio/0
167 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 aio/1
168 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 aio/2
169 root 10 -5 0 0 0 S 0.0 0.0 0:00.00 aio/3
Example 4. Basic output of top
Top is an interactive tool that allows a system administrator to view the process table in order of CPU or memory usage, by user, and at varying refresh rates. For example, a system administrator who wants to monitor the process running under the user apache (option u, apache), sorted by memory usage (option M), updated every half second (option S, .5) would get that output. See Example 5, “Example of top output sorted by user apache”.
top - 23:58:42 up 3:33, 1 user, load average: 0.00, 0.00, 0.00 Tasks: 88 total, 1 running, 87 sleeping, 0 stopped, 0 zombie Cpu(s): 0.0% us, 0.0% sy, 0.0% ni, 100.0% id, 0.0% wa, 0.0% hi, 0.0% si Mem: 2055112k total, 227436k used, 1827676k free, 53740k buffers Swap: 2096472k total, 0k used, 2096472k free, 101220k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1911 apache 16 0 113m 13m 7984 S 0.0 0.7 0:00.00 httpd 1912 apache 15 0 113m 13m 7980 S 0.0 0.7 0:00.00 httpd 1913 apache 16 0 113m 12m 7912 S 0.0 0.6 0:00.00 httpd 1914 apache 20 0 113m 12m 7912 S 0.0 0.6 0:00.00 httpd 1915 apache 20 0 113m 12m 7912 S 0.0 0.6 0:00.00 httpd 1916 apache 20 0 113m 12m 7912 S 0.0 0.6 0:00.00 httpd 1917 apache 20 0 113m 12m 7912 S 0.0 0.6 0:00.00 httpd 1918 apache 25 0 113m 12m 7912 S 0.0 0.6 0:00.00 httpd
Example 5. Example of top output sorted by user apache
Top is useful for viewing real-time process behavior within the context of system resources. The use of a faster refresh rate will provide enhanced precision for measuring system loads. For example, if you have a system running an Oracle® Database, and your startup time for the database is unacceptably slow, you will be able to see what processes consume a greater part of memory while the system is pegged. While top is a good interactive tool, you may not have the time or inclination to sit and watch processes for more than a few minutes. Luckily, there’s more.
Sar, yes, sar!
Sar is one of those utilities that conjures up images of UNIX nerds that took Latin in high school (when Latin was still offered in high schools). Because of sar‘s relative oddness, it is often lumped into the same category as sendmail for ease of configuration. To be fair, there is wonderful documentation for most such utilities. However, looking beyond sar‘s reputation for obscurity in output as well as syntax reveals a powerful system monitoring tool.
You can install sar by installing the sysstat package with the command yum install sysstat. You also need to initialize sar the first time by running /usr/lib/sa/sa1 1 1 and /usr/lib/sa/sa2 -A, or by letting cron run these commands. The sysstat package will place these in /etc/cron.d/systat/, and you won’t be able to run sar with no arguments and get meaningful output without having done this first.
Running sar with no arguments will give you some pretty obvious output as to what’s going on in your system. In Example 6, “Basic output of sar”, we see the day’s cumulative averages so far for every ten minutes on all CPUs. You will notice that these are the same pieces of information that we saw in top, except that in this case, sar gives us a time breakdown of when loads occurred.
Linux 2.6.12-1.1398_FC4smp (knuth) 08/28/2005 12:00:01 AM CPU %user %nice %system %iowait %idle 12:10:01 AM all 0.01 0.00 0.01 0.00 99.98 12:20:01 AM all 0.01 0.00 0.01 0.00 99.98 12:30:01 AM all 0.01 0.00 0.01 0.01 99.98 12:40:01 AM all 0.00 0.00 0.00 0.00 100.00 12:50:01 AM all 0.00 0.00 0.00 0.01 99.99 01:00:01 AM all 0.00 0.00 0.00 0.00 100.00 01:10:01 AM all 0.00 0.00 0.00 0.00 100.00 01:20:01 AM all 0.00 0.00 0.00 0.00 100.00 01:30:01 AM all 0.00 0.00 0.00 0.00 100.00 01:40:01 AM all 0.00 0.00 0.00 0.00 100.00 01:50:01 AM all 0.00 0.00 0.00 0.00 100.00 Average: all 0.00 0.00 0.00 0.00 99.99
Example 6. Basic output of sar
Incidentally, these values are stored by running sar in cron. Fedora™ Core 4 has the following entries in /etc/cron.d/sysstat, by default:
# run system activity accounting tool every 10 minutes */10 * * * * root /usr/lib/sa/sa1 1 1 # generate a daily summary of process accounting at 23:53 53 23 * * * root /usr/lib/sa/sa2 -A
The sa1 script collects and stores binary data in the system activity daily data file, and sa2 writes a daily report in the /var/log/sa/ directory. Sar can also be invoked to provide real-time statistics on the fly. In Example 7, “Example output of sar 1 10”, I have invoked sar with the options for a one second interval over 10 iterations. This is a very effective way to evaluate where a bottleneck might lie. If you’re having problems with I/O wait when certain reads take place, you’ll be able to see it here. Running sar in this fashion offers you the dynamic output of top with the specificity of sar. See Example 7, “Example output of sar 1 10”.
Linux 2.6.12-1.1398_FC4smp (knuth) 08/28/2005 02:13:43 AM CPU %user %nice %system %iowait %idle 02:13:44 AM all 0.00 0.00 0.00 0.00 100.00 02:13:45 AM all 0.00 0.00 0.00 0.00 100.00 02:13:46 AM all 0.00 0.00 0.00 0.00 100.00 02:13:47 AM all 0.00 0.00 0.00 0.00 100.00 02:13:48 AM all 0.00 0.00 0.00 0.00 100.00 02:13:49 AM all 0.00 0.00 0.00 0.00 100.00 02:13:50 AM all 0.00 0.00 0.00 0.00 100.00 02:13:51 AM all 0.00 0.00 0.00 0.00 100.00 02:13:52 AM all 0.00 0.00 0.00 0.00 100.00 02:13:53 AM all 0.00 0.00 0.00 0.00 100.00 Average: all 0.00 0.00 0.00 0.00 100.00
Example 7. Example output of sar 1 10
Sar also allows you to view the same output but restricts your reporting to a particular processor. Example 8, “sar -P 1 1 5 output” shows 5 one second iterations for CPU 1, and Example 9, “sar -P 2 1 5 output” shows 5 one second iterations for CPU 2.
Linux 2.6.12-1.1398_FC4smp (knuth) 08/28/2005 02:28:24 AM CPU %user %nice %system %iowait %idle 02:28:25 AM 1 0.00 0.00 0.00 0.00 100.00 02:28:25 AM CPU %user %nice %system %iowait %idle 02:28:26 AM 1 0.00 0.00 0.00 0.00 100.00 02:28:26 AM CPU %user %nice %system %iowait %idle 02:28:27 AM 1 0.00 0.00 0.00 0.00 100.00 02:28:27 AM CPU %user %nice %system %iowait %idle 02:28:28 AM 1 0.00 0.00 0.00 0.00 100.00 02:28:28 AM CPU %user %nice %system %iowait %idle 02:28:29 AM 1 0.00 0.00 0.00 0.00 100.00 Average: CPU %user %nice %system %iowait %idle Average: 1 0.00 0.00 0.00 0.00 100.00
Example 8. sar -P 1 1 5 output
Linux 2.6.12-1.1398_FC4smp (knuth) 08/28/2005 02:28:33 AM CPU %user %nice %system %iowait %idle 02:28:34 AM 2 0.00 0.00 0.00 0.00 100.00 02:28:34 AM CPU %user %nice %system %iowait %idle 02:28:35 AM 2 0.00 0.00 0.00 0.00 100.00 02:28:35 AM CPU %user %nice %system %iowait %idle 02:28:36 AM 2 0.00 0.00 0.00 0.00 100.00 02:28:36 AM CPU %user %nice %system %iowait %idle 02:28:37 AM 2 0.00 0.00 0.00 0.00 100.00 02:28:37 AM CPU %user %nice %system %iowait %idle 02:28:38 AM 2 0.00 0.00 0.00 0.00 100.00 Average: CPU %user %nice %system %iowait %idle Average: 2 0.00 0.00 0.00 0.00 100.00
Example 9. sar -P 2 1 5 output
Check your system, STAT!
There are a number of *stat commands that appear in any given system, and I would like to mention two which I think are most useful. The first of these is iostat. Iostat reports CPU statistics and input/output statistics for devices and partitions. While it seems that CPU statistics are available in every utility mentioned here so far, it’s the I/O part of iostat that makes it useful. Iostat run without any parameters gives you a single history since boot report for all CPU and devices. This is useful for a quick look at device utilization and, in this case, looking at CPU usage makes a lot of sense. In Example 10, “Basic output of iostat”, iostat shows blocks read and written per second and overall.
Linux 2.6.12-1.1398_FC4smp (knuth) 08/28/2005
avg-cpu: %user %nice %sys %iowait %idle
0.01 0.00 0.01 0.04 99.93
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 0.92 12.27 8.27 289810 195288
Example 10. Basic output of iostat
In Example 11, “Output of iostat -p sda 1 3”, iostat displays three reports at one second intervals for device sda and all its partitions. It’s easy to see how iostat can deliver real-time statistics on the partitions’ reads and writes.
Linux 2.6.12-1.1398_FC4smp (knuth) 08/28/2005
avg-cpu: %user %nice %sys %iowait %idle
0.01 0.00 0.01 0.04 99.93
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 0.92 12.08 8.36 289810 200592
sda3 0.01 0.02 0.00 386 0
sda2 1.68 12.01 8.36 288138 200544
sda1 0.02 0.04 0.00 1024 48
avg-cpu: %user %nice %sys %iowait %idle
0.00 0.00 0.00 0.00 100.00
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 0.00 0.00 0.00 0 0
sda3 0.00 0.00 0.00 0 0
sda2 0.00 0.00 0.00 0 0
sda1 0.00 0.00 0.00 0 0
avg-cpu: %user %nice %sys %iowait %idle
0.00 0.00 0.00 0.00 100.00
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 0.00 0.00 0.00 0 0
sda3 0.00 0.00 0.00 0 0
sda2 0.00 0.00 0.00 0 0
sda1 0.00 0.00 0.00 0 0
Example 11. Output of iostat -p sda 1 3
The last utility I would like to mention is vmstat. Vmstat reports statistics on virtual memory and can be useful when trying to identify system bottlenecks. Vmstat does not count itself as a running process, and it can be used in a number of modes. Run with no parameters, vmstat will display active and inactive memory. Like iostat, vmstat can be run in iterations, at a particular interval. In Example 12, “Output of vmstat 1 5”, vmstat is run at one second intervals for five iterations.
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 1826368 57028 102352 0 0 1 1 251 6 0 0 100 0 0 0 0 1826368 57028 102352 0 0 0 0 1008 13 0 0 100 0 0 0 0 1826368 57028 102352 0 0 0 0 1004 13 0 0 100 0 0 0 0 1826368 57036 102344 0 0 0 60 1007 25 0 0 100 0 0 0 0 1826368 57036 102344 0 0 0 0 1004 13 0 0 100 0
Example 12. Output of vmstat 1 5
Vmstat can also provide a quick list of memory-related statistics from the vmstat -s command:
2055112 total memory
229240 used memory
84480 active memory
91816 inactive memory
1825872 free memory
57224 buffer memory
102156 swap cache
2096472 total swap
0 used swap
2096472 free swap
1130 non-nice user cpu ticks
247 nice user cpu ticks
1110 system cpu ticks
9995941 idle cpu ticks
3860 IO-wait cpu ticks
35 IRQ cpu ticks
56 softirq cpu ticks
144945 pages paged in
108540 pages paged out
0 pages swapped in
0 pages swapped out
25092942 interrupts
575618 CPU context switches
1126139091 boot time
4447 forks
as well as partition information from the vmstat -p sda2:
sda2 reads read sectors writes requested writes
15200 288218 27285 218280
Many of the functions of the utilities discussed in this article overlap. This is the result of having several authors who have attempted to provide you with as elegant and powerful a utility as possible. This has the potential, however, of causing some confusion or apathy in using these tools because they seem redundant or are perceived to be “bloated.” However, the system administrator, who recognizes each tool for its strengths and inherent ability to report cleanly the characteristics of a running system, will find that their system comes with a rather complete tool set for not only reacting to but predicting performance issues via proactive monitoring.
About the author
Hotlink protection: How-To prevent people from stealing your files
by dino on May.25, 2008, under Basics, Command Line, DirectAdmin, Plesk, Virtuozzo, WebMin, cPanel
Create an .htaccess file in your public_html directory with the following code:
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www.)?domain.com.*$ [NC]
RewriteRule .(gif|jpg)$ – [F]
Where domain.com is your domain.
semget: No space left on device
by dino on Apr.25, 2008, under Basics, Command Line, DirectAdmin, Plesk, Uncategorized, Virtuozzo, WebMin, cPanel
This relates to semaphores on your system (you’ve run out). Run the following to clear them out:
ipcs | grep apache | awk ‘{print $2}’ > sem.txt
for i in `cat sem.txt`; do { ipcrm -s $i; }; done;
For cPanel servers :
ipcs | grep nobody | awk ‘{print $2}’ > sem.txt
for i in `cat sem.txt`; do { ipcrm -s $i; }; done;
Finally restart Apache :
/etc/init.d/httpd restart
service httpd restart
Service/Daemon Management
by admin on Mar.06, 2008, under Basics
restarting/stopping/starting a service
On any init.d based linux distro you can restart a service with the following…
/etc/init.d/serviceName restart
You may replace ‘restart’ with ’stop’ or ’start’ (and in some cases ’status’).
Forcefully stopping a service
killall processName
Killing on instance of a service
kill pid
The pid can be gathered by either top or ps
Disabling/adding/listing services
chkconfig –list
displays all the services and if they are set to run in different runlevels
use the –del daemonName to remove a service or –add daemonName to add one
chkconfig [--level <levels>] <name> <on|off|reset>
eg. chkconfig –level 3 httpd on
This will set the httpd to ON on run level 3.
setting a program to run at startup
Add a line executing the command at the end of /etc/rc.local
File Manipulation
Editing Text Files
vi is by far the best text editor but has a learning curve to it. If you want simplicity use nano
display a text file from the command line
cat filename
or
more filename
Display the last few lines of a text file
tail filename
or you can display the last 50 lines of a file with…
tail -50 filename
or you can display lines as they are written to a file (or follow) with the following: (UBER useful for log files)
tail -f filename
copy a file
cp filename destination
move a file
mv filename destination
delete a file
rm -f filename : removes the file. -f makes it so it doesn’t ask you if you are sure
Displaying the differences between two files
diff file1 file2
Installing crap
On redhat derived systems (RedHat, Fedora, CentOS, Rocks, Mandrake, etc) yum is your package manager.
yum install appname : installs the application from the remote yum repository
yum search appname : does a search on the repository for a given program
yum remove appname : uninstalls an app
use ‘man yum’ for a complete list
Archives
tar.gz or .tgz is the most common compression found in the linux world. that is tared (Tape ARchive) and gziped. Sometimes called “tar balls”.
tar -xzf file.tgz : will X’trackt a tar/gzip file.
tar -czf myfile.tgz someDir : will create a tar and gziped archive of the given directory
gunzip : un gzips a file
unzip : unzips a .zip file
User Management
by admin on Mar.06, 2008, under Basics
useradd
useradd userName
then run “passwd userName” to set the new users pw
passwd
passwd username
will ask for the new pw twice
File Permissions
by admin on Mar.06, 2008, under Basics
Listing Permissions
ls -al will display all files in a list with their owners and permissions
-rw-r–r– 1 irq13 irq13 1006 Jan 24 10:16 .bashrc
Now to break down the above example…
-rw-r–r– is the permissions area.
The first – would be d if the item is directory, otherwise it will be -.
The second 3 dashes indicate read/write/execute for the owner,
the second is r/w/x for the group and third is r/w/x for everyone else.
The next number is the inodes associated with the file. This isn’t important for you to know the basics
Next when it says irq13 irq13 that indicates the owner of the files name group
Changing ownership of a file
chown username:groupname file
Changing permissions of a file
chmod XXX filename
chmod uses a numeric system for assigning ownership.
XXX represents 3 numbers.
The first is the permissions applied to the owning user, 2nd is group, 3rd is everyone else.
1: execute 2: write 3: write & execute 4: read 5: read & execute 6: read & write 7: read, write & execute
Remember that 777 is only to be used as a trouble shooting step to rule fs permissions out.
NEVER leave a dir as 777. Its useful to do ‘ls -alh * > perm_capture.txt’ before messing with a file.
That way you can restore its original permissions.
Attributes
Files also have attributes, similar to the ones found in the windows world.
lsattr filename : Lists the attributes of a file or directory
chattr +-=[ASacDdIijsTtu] filename
to add an attribute use + to remove use -
File Attributes
append only (a)
compressed (c)
no dump (d)
immutable (i)
data journaling (j)
secure deletion (s)
no tail-merging (t)
undeletable (u)
no atime updates (A)
synchronous directory updates (D)
syn-chronous updates (S)
top of directory hierarchy (T)
Use man chattr for an explanation of each attribute
launching scripts and bins
* If an executable file is in your path you may simply type its name from anywhere on the system and it will execute.
* To see what your path is type ‘path’
* To execute a file in the current directory type “./filename
* To execute a file it must have execute permissions for either your username or a group you belong to.
Additional command operators
by admin on Mar.06, 2008, under Basics
ps | grep ssh — only display lines that contain ssh
; used to “stack commands” or issue multiple commands on 1 line. cd ..; ls
& puts a command in the background. Will let you know when the command is finished
> write what is displayed on the screen from a given command to a text file ls -alh /root > /root/myRoot.txt
>>
appends screen output to an existing file
-
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