Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs.

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5answers
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How to Chown a directory recursively including hidden files or directories

Seems like chown with the recursive flag will not work on hidden directories or files. Is there any simple workaround for that?
19
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4answers
17k views

How to pipe stderr without piping stdout

How do I pipe the standard error stream without piping the standard out stream? I know this command works, but it also writes the standard out. Command 2>&1 | tee -a $LOG How do I get ...
19
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2answers
27k views

Getting the last match in a file using grep

What's the best way of getting only the final match of a regular expression in a file using grep? Also, is it possible to begin grepping from the end of the file instead of the beginning and stop ...
19
votes
2answers
14k views

Better logging for cronjobs? Send cron output to syslog?

I am looking for a better way to log cronjobs. Most cronjobs tend to spam email or the console, get ignored, or create yet another logfile. In this case, I have a Nagios NSCA script which sends data ...
18
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7answers
47k views

How to disable everything in crontab -l?

I just want to pause everything. Don't execute anything listed on crontab -l.
18
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9answers
26k views

How can I find the biggest directories in unix / Ubuntu?

Is there a way in Unix to see the biggest directories on disk ? I need to know why I'm almost done with the space on the server, and I dunno where most of the space is used.. thanks
18
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2answers
14k views

What is the sticky bit in UNIX file systems? When is it used?

What is the sticky bit in a UNIX file system? As an admin when and how would you use it?
17
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4answers
9k views

What is the “slash” after the IP?

In Amazon EC2, where I set "security groups", It says: Source: 0.0.0.0/0 And then it gives an example of: 192.168.2.0/24 What is "/24"? I know what port and IP is.
17
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6answers
56k views

How to change owner of mount point

We have moved mysql data directory to another disk, so now /var/lib/mysql is just a mount point to another partition. We set the owner of the /var/lib/mysql directory to mysql.mysql. But everytime we ...
17
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9answers
2k views

Is there a paging version of `watch`?

Under a UNIX shell, how can I get a similar effect to the watch command, but with paging so that I can scroll around in the output if it takes up more than one screen? In other words, I want a ...
17
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3answers
7k views

To fsck or not fsck after 180 days

By default after 180 days or some number of mounts, most Linux filesystems force a file system check (fsck). Of course this can be turned off using, for example, tune2fs -c 0 -i 0 on ext2 or ext3. On ...
17
votes
4answers
3k views

What's the best way to clean up after a fork bomb?

$ ls bash: no more processes Uh oh. Looks like someone made a fork bomb. Where I used to work, this pretty much meant that the shared server would need to be power-cycled, since even the sysadmins ...
16
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4answers
24k views

How can I run mongod in the background on unix (mac osx)?

I would like to run mongod in the background as an always present sort of thing. What would be the best way to do this? Kind of like the way I can run MySQL on startup and it's just always there ...
16
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6answers
20k views

What's the maxium number of files a Unix folder can hold?

What's the maxium number of files a Unix folder can hold? I think it will be the same as the number of files.
16
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2answers
2k views

Linux/Debian - What does 'pee' in moreutils do?

I recently discovered the 'moreutils' package in Debian (and Ubuntu). It's a collection of convenient unix tools. One of the commands is 'pee'. The man page says: pee is like tee but for pipes. ...
16
votes
4answers
14k views

What are the advantages/disadvantages of hard versus soft mounts in UNIX?

This question may vary between distros but, in general, what are the advantages/disadvantages of using a hard or soft mount in the UNIX world? Are there certain situations where one is more ...
16
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6answers
10k views

Git - post-receive hook with git pull “Failed to find a valid git directory”

It's very weird but when setting a git repository and creating a post-receive hook with: echo "--initializing hook--" cd ~/websites/testing echo "--prepare update--" git pull echo "--update ...
16
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2answers
7k views

Making libmagic/file detect .docx files

As seen elsewhere, docx, xlsx and pttx are ZIPs. When uploading them to my web application, file (via libmagic andpython-magic) detects them as being ZIP. I store the contents of the file as a blob ...
15
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8answers
4k views

How many and which partitions should I create for a linux server?

Partitions are very important on Linux server because it give you a lot of flexibility, for example when upgrading to a bigger hard drive. But, how many partitions should I create when building a ...
15
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3answers
27k views

.nfsXXXX files appearing, what are those?

We have an application running (on RHEL5), streaming data onto an NFS share. Recently we saw a lot of .nfsXXXX... (xxx being a hexadecimal number) appearing in its working directory, where the ...
15
votes
3answers
7k views

Override MAILTO for a single crontab entry

We have a role account at work that has a pretty big crontab. Its MAILTO is pointed at a shared address, so that a number of us get notified if something fails. I'd like to add an entry to this ...
14
votes
5answers
47k views

How can I manually run a nagios check from the command line?

When defining and testing new services in nagios I have been restarting nagios, then clicking the service, and rescheduling a check for as soon as possible, then waiting until the check happens. Is ...
14
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5answers
1k views

Copy file permissions, but not files in Unix

(From : http://stackoverflow.com/questions/15245144/copy-file-permissions-but-not-files, closed because off-topic) I have two copies of the same directory tree. They almost have the same files in ...
14
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3answers
19k views

Getting rsync to move file from source to destination?

Is rsync is a good choice for my project ? I have to : - copy files from source to destination folder via SSH, - be sure all files are copied, - delete source files after copy. - if I have conflict ...
14
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3answers
2k views

Is there a mechanism in Unix (or Linux) to stop an in-progress core dump?

Let's say a (very) large process is crashing and dumping core, and we know the cause from other information (possibly an assert message, maybe something else). Is there a way to stop the core dump ...
13
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3answers
2k views

When should I use “nohup”, and when should I use “&”?

I never know when's the best time to use nohup and the & at the end of the command.
13
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6answers
2k views

Building a Linux Network for Our Company - Where Do I Start?

This is going to be a somewhat loaded question. I am programming in a company that has been around since 1962. A lot of things, especially computer / network stuff, is very dated. Let me give a bit ...
13
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2answers
15k views

When to use single-quote, double-quote in grep?

While trying to search for a simple pattern "hello" in a file, all the following forms of grep work: grep hello file1 grep 'hello' file1 grep "hello" file1 Is there a specific case where one of ...
13
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2answers
9k views

Create Unix Named Socket from the Command Line

Is there a command similar to mkfifo but for domain sockets?
13
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5answers
5k views

What are the practical differences between Interix and Cygwin?

Both Interix and Cygwin appear to provide a Unix-like user environment in Windows. What are the practical differences between the two, in terms of, for example: Unix-like "feel" Performance Package ...
12
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14answers
2k views

Why pay for UNIX?

I'm fairly new to Unicies. With the advent of GNU/Linux and BSDs, what are the reasons for companies to prefer AIX, Solaris and other commercial systems?
12
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4answers
2k views

how many user accounts can a unix-like OS host?

Let's say I want to have a server with as many user accounts as possible. How many is the max? I want millions of user accounts. Is that crazy? I'd host dozens of load-balance mirrors of the box, ...
12
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6answers
50k views

How to check what port mysql is running on

On my windows dev box mysql is running on port 3306 How can I check what port it is running on the unix server that I have to upload the app to.
12
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11answers
13k views

Best way to go about changing a root password on 3000+ Solaris, AIX, and Linux servers?

Long story short: Big old corporation, lots of UNIX/Linux servers. I inherited responsibility for a bunch of scripts that that left a few years ago. One of them was a script that would be run every ...
12
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8answers
22k views

Why can't I ssh into my new EC2 Instance?

I created a new instance (tiny, 64 bit AMI linux from Amazon) Created a new key pair called "mir". I downloaded mir.pem and put it in my ~/.ssh folder. I even did ssh-add mir.pem. Then I tried to ...
12
votes
1answer
4k views

Getting rsync to delete files from the *sender* after transfer

I'm using rsync to move one directory to another. Is there some way to get rsync to incrementally delete a file from the sender after it has copied it to the reciever?
12
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4answers
7k views

Does iowait include time waiting for network calls?

The proc(5) manpage describes iowait as "time waiting for IO to complete". This was mostly explained in an earlier question. My question is: while waiting in blocking IO, does this include waiting on ...
12
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1answer
407 views

Can you help me with my software dependency issue?

This is a Canonical Question about Compile Dependencies and Package Management. I have a question regarding compiling ports/software or installing RPMs on my *nix server. When I try to do this ...
11
votes
5answers
3k views

Where do you normally keep your UNIX/Linux scripts?

There are numerous scripts that I have written for my server. Some of them are in my ~/scripts and some of them are in application directories. I am just wondering is there a directory that you would ...
11
votes
6answers
3k views

Deleting a UNIX directory with a hyphen in the name

Through a boneheaded maneuver on my part, I accidentally created a directory called (for instance) -A, and ended up filling it with files. I want to delete said directory. I've tried: rmdir -- -A ...
11
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8answers
15k views

Is it possible to hide lost+found?

Given a partition intended solely for storing music, video and so-on, is it possible to hide the lost+found directory?
11
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9answers
5k views

Multiple *NIX Accounts with Identical UID

I am curious whether there is a standard expected behavior and whether it is considered bad practice when creating more than one account on Linux/Unix that have the same UID. I've done some testing on ...
11
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4answers
4k views

Available disk space on Unix/Linux OS

How to get available disk space on Unix/Linux OS, including unallocated space (which wasn't assigned to any partitions)?
11
votes
9answers
6k views

How do I master the UNIX find command?

I think I am fairly advanced in my use of find but EVERY time I use it I cannot for the life of me remember the method to close the -exec option. I spend a good deal of time reading every time I use ...
11
votes
3answers
12k views

How can I rename an unix user?

I have a user named hedgehog and I want him to be named squirrel, but I don't want to change his numeric user ID. How can I accomplish this?
11
votes
5answers
5k views

Specify default group and permissions for new files in a certain directory

I have a certain directory in which there is a project shared by multiple users. These users use SSH to gain access to this directory and modify/create files. This project should only be writeable to ...
11
votes
4answers
7k views

When would ssh -t not be appropriate instead of ssh?

Using ssh -t instead of ssh for connections to remote servers has several advantages. For example, I can directly edit a file with vim: ssh -t host vim foo.txt, which would fail otherwise. Are there ...
11
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5answers
12k views

How do I list a file's data blocks on Linux?

As I understand it, each file on a Unix-like operating system has an inode number (which can be viewed with "ls -i"), and each inode is a list of disk blocks that contain the actual data of a file. ...
11
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3answers
489 views

How do I delete all empty directories

(on a Linux system) I have a large set of nested subdirectories on a filesystem. I would like to prune all directory paths that contain no files at all. In other words I would like to delete every ...
11
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5answers
5k views

Confused by CPU values in Unix 'top' command

In the screenshot below, the overall CPU is being reported as 3% but the mysqld process is reported as using 57%. Is this 57% of the overall 3% and thus mysqld is only using about 1.5% of the CPU? ...