16
votes
3answers
28k views

How to install program locally without sudo privileges?

Assume I have ssh access to some Ubuntu server as user and I need some not system tools to be installed for convenience (mc, rtorrent, mcedit). I do not want to bother admins for these small programs. ...
13
votes
4answers
4k views

Is it possible to find out what program or script created a given file?

Three files have suddenly appeared in my home directory, called "client_state.xml", "lockfile", and "time_stats_log". The last two are empty. I'm wondering how they got there. It's not the first time ...
26
votes
1answer
8k views

How can I execute `date` inside of a cron tab job?

I want to create a log file for a cron script that has the current hour in the log file name. This is the command I tried to use: 0 * * * * echo hello >> ~/cron-logs/hourly/test`date "+%d"`.log ...
190
votes
10answers
22k views

In Bash, when to alias, when to script, and when to write a function?

It's taken me almost 10 years of Linux usage to ask this question. It was all trial and error and random late-night internet surfing. But people shouldn't need 10 years for this. If I were just ...
30
votes
3answers
2k views

Can a bash script be hooked to a file?

I want a script to sleep unless a certain file is modifed/deleted (or a file created in a certain directory, or ...). Can this be achieved in some elegant way? The simplest thing that comes to my mind ...
7
votes
2answers
7k views

I added a user to a group, but group permissions on files still have no effect

I changed permissions of a file (chmod g+w testfile) and running ls -l testfile gives: -rwxrwxr-x 1 user1 user1 0 2011-01-24 20:36 testfile I then added a user to that group ("/etc/group" has ...
45
votes
4answers
6k views

How to use `which` on an aliased command?

Like most users, I have a bunch of aliases set up to give a default set of flags for frequently used programs. For instance, alias vim='vim -X' alias grep='grep -E' alias ls='ls -G' The problem is ...
26
votes
4answers
43k views

Why do we use “./” to execute a file?

Why do we use ./filename to execute a file in linux? Why not just enter it like other commands gcc, ls etc...
82
votes
3answers
46k views

How do I read from /proc/$pid/mem under Linux?

The Linux proc(5) man page tells me that /proc/$pid/mem “can be used to access the pages of a process's memory”. But a straightforward attempt to use it only gives me $ cat /proc/$$/mem ...
83
votes
13answers
33k views

Get exit status of process that's piped to another

I have two processes foo and bar, connected with a pipe: $ foo | bar bar always exits 0; I'm interested in the exit code of foo. Is there any way to get at it?
28
votes
1answer
2k views

Why does my regular expression work in X but not in Y?

I wrote a regular expression which works well in a certain program (grep, sed, awk, perl, python, ruby, ksh, bash, zsh, find, emacs, vi, vim, gedit, …). But when I use it in a different program (or on ...
21
votes
1answer
3k views

Configuring, compiling and installing a custom Linux kernel

I'd like to try using a kernel other than the one provided by my distro -- either from somewhere else, or as customized by me. Is this difficult or dangerous? Where do I start?
16
votes
7answers
1k views

What is the difference between $* and $@?

Consider the following code: foo () { echo $* } bar () { echo $@ } foo 1 2 3 4 bar 1 2 3 4 It outputs: 1 2 3 4 1 2 3 4 I am using Ksh88, but I am interested in other common ...
28
votes
4answers
14k views

How can I make iconv replace the input file with the converted output?

I have a bash script which enumerates through every *.php file in a directory and applies iconv to it. This gets output in STDOUT. Since adding the -o parameter ( in my experience ) actually writes ...
16
votes
4answers
7k views

Wrongly set chmod / 777. Problems?

I was trying to run chmod -R 777 ./ but ended up typing chmod -R 777 / and set 777 on my entire machine. What can go wrong? How can I fix it?
9
votes
3answers
3k views

How to run a command when a directory's contents are updated?

There is a directory A whose contents are changed frequently by other people. I have made a personal directory B where I keep all the files that have ever been in A. Currently I just occasionally ...
9
votes
3answers
4k views

Automating web requests using curl?

I have some "corporative" systems I have to use at work. Some of them are terrible, with frames, pop-ups and such. I was thinking about automating some stuff using curl or something like that. I need ...
193
votes
12answers
156k views

What if 'kill -9' does not work?

I have a process I can't kill with kill -9 <pid>. What's the problem in such a case, especially since I am the owner of that process. I thought nothing could evade that kill option.
111
votes
7answers
26k views

Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?

I notice that some scripts which I have acquired from others have the shebang #!/path/to/NAME while others (using the same tool, NAME) have the shebang #!/usr/bin/env NAME. Both seem to work ...
61
votes
7answers
11k views

dd vs cat — is dd still relevant these days?

I recently realized we can use cat as much as dd, and it's actually faster than dd I know that dd was useful in dealing with tapes where block size actually mattered in correctness, not just ...
34
votes
3answers
60k views

How to make a machine accessible from the LAN using its hostname

Here are details of the machine I want to access using its hostname: $ hostname hostname $ cat /etc/hosts 127.0.0.1 localhost 127.0.1.1 hostname.company.local hostname It's a default Debian 6 ...
27
votes
1answer
2k views

How do keyboard input and text output work?

Suppose I press the A key in a text editor and this inserts the character a in the document and displays it on the screen. I know the editor application isn't directly communicating with the hardware ...
22
votes
6answers
13k views

Removing control chars (including console codes / colours) from script output

I can use the "script" command to record an interactive session at the command line. However, this includes all control characters and colour codes. I can remove control characters (like backspace) ...
28
votes
3answers
21k views

Why can't a normal user `chown` a file?

Why is the chown command root-only? Why can't non-root users use chown to give away files they own?
6
votes
2answers
1k views

How to make password-less login work

I generated a key and copied it to my target: ssh-keygen ssh-copy-id username@hostname I left the the location of the key as default and did not set any passphrase. For a small while after that, I ...
99
votes
19answers
136k views

Why am I still getting a password prompt with ssh with public key authentication?

I'm working from the URL I found here: http://jaybyjayfresh.com/2009/02/04/logging-in-without-a-password-certificates-ssh/ My ssh client is Ubuntu 64 bit 11.10 desktop and my server is Centos 6.2 64 ...
107
votes
7answers
75k views

How can I close a terminal without killing the command running in it?

Sometimes I want to start a process and forget about it. If I start it from the command line, like this: redshift I can't close the terminal, or it will kill the process. Can I run a command in ...
48
votes
3answers
61k views

Make all new files in a directory accessible to a group

Suppose I have two users A and B and a group G and a folder foo, both users are members of G (using linux and ext3). If I save as user A a file under foo, the permissions are: -rw-r--r-- A A. ...
34
votes
3answers
9k views

using single or double bracket - bash

I'm confused with using single or double bracket. look at code: dir="/home/mazimi/VirtualBox VMs" if [[ -d ${dir} ]]; then echo "yep" fi It works perfectly although the string contains space. ...
12
votes
3answers
27k views

Output traffic on different interfaces based on destination port

My question is basically the same as Only allow certain outbound traffic on certain interfaces. I have two interfaces eth1 (10.0.0.2) and wlan0 (192.168.0.2). My default route is for eth1. Let's say ...
31
votes
8answers
7k views

Non-Root Package Managers

From my research, I seem to notice that all package managers insist on being used as a privileged user and must be installed into /. Typically, what I like to do is create a throwaway account, ...
24
votes
2answers
7k views

Using an already established SSH channel

I have an already established ssh connection between two machines. Is there a way to send commands to the remote machine from a shell script that is run on the local machine, using the already open ...
7
votes
4answers
25k views

Storing output of command in shell variable [duplicate]

I have an operation using cut that I would like to assign result to a variable var4=echo ztemp.xml |cut -f1 -d '.' I get the error: ztemp.xml is not a command The value of var4 never gets ...
3
votes
1answer
26k views

How can I fix/install/reinstall grub?

So I started out with a 250GB HDD, the stock drive from an EeePC 1015pem that I am trying to turn into a MintBook. The drive is physically operable, but all data has been nuked, including the old OS. ...
5
votes
1answer
351 views

How to ensure that string interpolated into `sed` substitution escapes all metachars

I have a script that reads a text stream and generates a file of sed commands that is later run with sed -f. The generated sed commands are like: ...
72
votes
3answers
43k views

How does reverse SSH tunneling work?

As I understand this, firewalls (assuming default settings) deny all incoming traffic that has no prior corresponding outgoing traffic. Based on Reversing an ssh connection and SSH Tunneling Made ...
98
votes
2answers
17k views

When was the shellshock (CVE-2014-6271/7169) bug introduced, and what is the patch that fully fixes it?

Some context about the bug: CVE-2014-6271 Bash supports exporting not just shell variables, but also shell functions to other bash instances, via the process environment to (indirect) child ...
79
votes
3answers
42k views

What does “LC_ALL=C” do?

What does the C value for LC_ALL do in Unix-like systems? I know that it forces the same locale for all aspects but what does C do?
32
votes
4answers
5k views

Using '.' to execute files in bash

What's the difference between executing a script like this: ./test.sh and executing a script like this: . test.sh? I tried a simple, two-line script to see if I could find if there was a ...
20
votes
1answer
4k views

When is double-quoting necessary?

The old advice used to be to double-quote any expression involving a $VARIABLE, at least if one wanted it to be interpreted by the shell as one single item, otherwise, any spaces in the content of ...
28
votes
5answers
22k views

How to determine which process is creating a file?

Given file path, how can I determine which process creates it (and/or reads/writes to it)?
25
votes
3answers
18k views

Understanding IFS

The following few threads on this site and StackOverflow were helpful for understanding how IFS works: What is IFS in context of for looping? How to loop over the lines of a file Bash, read line by ...
30
votes
8answers
7k views

Is there a way to modify a file in-place?

I have a fairly large file (35Gb), and I would like to filter this file in situ (i.e. I don't have enough disk space for another file), specifically I want to grep and ignore some patterns — is there ...
32
votes
4answers
9k views

When would you use an additional file descriptor?

I know you can create a file descriptor and redirect output to it. e.g. exec 3<> /tmp/foo # open fd 3. echo a >&3 # write to it exec 3>&- # close fd 3. But you can do the same ...
11
votes
9answers
28k views

Automatically run commands over SSH on many servers

There is a list of IP addresses in a .txt file, ex.: 1.1.1.1 2.2.2.2 3.3.3.3 Behind every IP address there is a server, and on every server there is an sshd running on port 22. Not every server is ...
12
votes
1answer
1k views

Why is my bash prompt getting bugged when I browse the history?

Often when I start looking at history of commands some of the characters from a command displayed aren't erased, for example: What's happening: prompt$ some_command prompt$ some_commanother_command ...
9
votes
4answers
2k views

Is GRUB the best bootloading solution? Is there an easier alternative?

I have had some rather bad experiences with GRUB2. I could say (and have said) some nasty things about its design and development process. I especially dislike its means of update: for whatever reason ...
10
votes
2answers
4k views

real memory usage

if I understand correctly, in the following output produced by free, 3535m is the actual free memory available to applications, only 413m is used, is this correct? need some clarification on the ...
186
votes
2answers
42k views

Difference between nohup, disown and &

What is the difference between $ nohup foo and $ foo & and $ foo & $ disown
107
votes
9answers
10k views

The myths about malware in Unix / Linux

Is it possible for my Linux box to become infected with a malware? I haven't heard of it happening to anyone I know, and I've heard quite a few times that it isn't possible. Is that true? If so, ...

15 30 50 per page