Questions tagged [lock]
The lock tag has no usage guidance.
21
votes
3answers
2k views
How does this script ensure that only one instance of itself is running?
On 19 Aug 2013, Randal L. Schwartz posted this shell script, which was intended to ensure, on Linux, "that only one instance of [the] script is running, without race conditions or having to clean up ...
1
vote
0answers
21 views
About `page_table_lock` in Linux process address space
I'm reading a tutorial about Linux page table, in the linked page
Each process has its own page tables (threads share them). The pgd field of the memory descriptor points to the process's page ...
2
votes
0answers
48 views
Lock Virtual Terminals when resuming
Many screen lockers (mine is i3lock) do not block access to other Virtual Terminals. This means that, if I leave a session opened in some VT, then even when the desktop is locked (for example when ...
0
votes
0answers
78 views
Does pid file work by assuming pid is not usable?
To use a pid file for ensuring singleton running instance of a program, I thought that when a process finishes running the program, it should remove the pid file, until I know it doesn't when reading ...
0
votes
1answer
29 views
Can we tell if a command is being run by a process or not, by looking at the flock lock file alone?
Is util-linux's flock implemented based on flock() in Linux C API?
Can we tell if a command is being run by a process or not, by looking at the lock file alone?
I found that when a command guarded by ...
1
vote
1answer
70 views
Is pseudo terminals ( unlockpt / TIOCSPTLCK ) a security feature?
After having opened the master part of a pseude-terminal
int fd_pseudo_term_master = open("/dev/ptmx",O_RDWR);
there is the file /dev/pts/[NUMBER] created, representing the slave part of he pseudo-...
-1
votes
1answer
55 views
Why “a lock file is the best approach if the resource is not a regular file, so using methods for locking files does not apply”?
Thanks to Mark's comment, pointing me to https://en.wikipedia.org/wiki/File_locking#Lock_files which says
Shell scripts and other programs often use a strategy similar to the use of file locking: ...
0
votes
1answer
83 views
Allow DPMS to turn off screen with force when the screen is locked?
I discover that command xset dpms 300 which turn off the screen for example after 5 minutes (300s), and it wonderfully doesn't turn off the screen if a youtube video is actually playing even in a ...
1
vote
2answers
474 views
SELinux - How to avoid it preventing a process from write access on newly created files into folder
I'm hardly trying to correctly use selinux keeping it in enforced mode, but very often I encounter issues with it causing our application to work improperly.
Our web application is java backend and ...
1
vote
1answer
46 views
Where is official documentation about locking mechanisms for etckeeper, apt, and/or dpkg?
Context:
Want to put a lock on etckeeper/apt hook activity during special backup.
Objective is to preserve whole package integrity, e.g., wait until any package installation is complete, and then ...
0
votes
2answers
36 views
Getting Information about locks associated with a process
I am unable to list the locks associated with a process and information about the locks i.e How many threads share this lock etc.
Kindly tell my how to extract this information from a process ID.
My ...
-1
votes
3answers
47 views
Locking user account in a specific way
I've been tasked with performing a lockdown on a user account (making it impossible to properly login-in to) in a very specific way. Im prohibited from:
a) Altering his password (so passwd -l is out ...
1
vote
2answers
745 views
some other process automatically locks /var/lib/dpkg/lock for few minutes when restarting my system.
I am running Debian buster a.k.a. Debian testing. From the last couple of weeks, whenever I reboot the sytem i.e. going to CTRL+ALT+F1 and run
$ sudo reboot
it reboots the systems as normally but ...
1
vote
1answer
290 views
Create lock using unix socket/port
Is there a way to hold a lock a unix port using netcat or some other command?
I want to do something like this:
set -e;
nc -lock 8000 & # this needs to fail if another process holds the lock
...
-1
votes
1answer
327 views
How can I simulate locking a file?
I would like to lock a file, run some tests then unlock the file. How can I do this. I could use the command line, perl, or a shell script.
The reason I would like to lock the file is occasionally ...
1
vote
1answer
77 views
fcntl delete behaviour
I have a requirement to create locks via fcntl to make a script run only once with a given argument.
To achieve this, I create a file with the given argument and acquire lock on it.
I have the below ...
1
vote
1answer
191 views
Slackware 14.2 - black screen after waking from sleep/lock - what process controls sleep/lock?
I have had Slackware 14.2 32bit installed on a netbook with LXDE as my main DE for about a month now. My main issue is that sometimes the screen is black on waking from sleep [suspend] and the only ...
0
votes
1answer
60 views
Basic spinlock doubt
I read that in spinlock, process keeps on waiting for the lock continuously in a loop until it receives signal(lock) or release(lock) from other process. This causes busy waiting and hence CPU cycles ...
3
votes
2answers
7k views
How do I kill the process holding the apt lock?
I tried doing
sudo apt update
but got:
Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable)
E: Unable to lock directory /var/lib/apt/lists/
I am trying ...
0
votes
1answer
1k views
Lock Usb Flash-Drive on Ubuntu Linux
By security request, I need to set up Ubuntu desktops from my network to not allow the use of flashdrives or USB storage devices. But the USB mouse and keyboard should normally be charged. Is there a ...
5
votes
1answer
4k views
Why flock doesn't clean the lock file? [closed]
After process is completed, I see that the lock file isn't deleted? Is there any reason that why flock keeps the file ? Also how does flock knows if there is a lock acquired ?
Here is the example ...
2
votes
1answer
709 views
Meaning of fcntl … F_SETLK … (Resource temporarily unavailable) in strace output?
When I use straceon Apache while it acts unresponsive, I get the following output:
[pid 13704] fcntl(57, F_SETLK, {type=F_RDLCK, whence=SEEK_SET, start=1073741824, len=1}) = -1 EAGAIN (Resource ...
3
votes
1answer
12k views
NFS mount: Device or resource busy
I referred the following link, the solution works.
How to get over "device or resource busy"?
The above solution works when you are manually deleting the file. But I have a python script ...
0
votes
1answer
605 views
Arch: safely save and restore pacman databases
I want to backup the pacman sync databases after an execution of pacman -Sy, creating "restore points" which pacman -Suu can use to reverse a failed system upgrade. Further background can be found ...
0
votes
0answers
46 views
atop - how to check what process locked folder during umount?
I have some software which unmounting folder during it's operation. But for some reason it can't do it. When I trying to umount folder manually (almost in same time) it does work. Can someone let me ...
3
votes
1answer
563 views
Check and Test Lock from other Process
I am trying to create a service wrapper (init.d script) around one of my favorite applications. The application creates both a PID and a lock file, and so I'm trying to use those to ensure that I can ...
2
votes
3answers
3k views
Does killing a process close all files opened by that process?
I want to kill a process which has an open connection to a database. If I kill the process, can I make sure that the database is unlocked?
1
vote
1answer
337 views
How to lock non-virtual terminal? Something like “vlock -a”"
There is an option with vlock to lock all pts/tty at a time which is,
$ vlock -a
But vlock can lock only virtual consoles.
There is also an option named TMOUT which will terminate the current ...
2
votes
1answer
1k views
lock screen session suspension in debian jessie
lock screen session suspension in debian jessie
I just read of an issue that seemed similar to mine, and as I cannot comment yet and my problem is different I will ask my question outright. the ...
0
votes
1answer
146 views
Duplication of a file descriptor associated with an fcntl lock?
According to the man page of dup2, this syscall make a new copy of the old file descriptor. The two descriptors do not share (the close-on-exec flag).
However in case the file descriptor we are ...
2
votes
1answer
6k views
How to do locking a file from a shell script? [duplicate]
I would like to synchronize two Bash scripts via a file lock. How to do this? Zsh has zsystem flock call, but is there a more "shellish" method that's also available to Bash?
-2
votes
1answer
459 views
readonly file on linux
I want to lock a file(or read-only) so that anybody on server can't modify it. I find chattr command on Linux but I didn't use it for some reason.
I am using mount --bind file.log file.log, but after ...
2
votes
0answers
421 views
How to use lockf on command line
I want to lock and unlock a file that resides in NFS share so I've found the reliable way is to go with lockf how can I use that in command line for flock I could do 'flock -s number' how can I do ...
3
votes
1answer
198 views
XScreenSaver: 1-2 seconds delay within which my laptop isn't locked
I want my screen to lock automatically and I'm using XScreenSaver. It locks the screen when my laptop suspends but when open the lid or press the power button, there's a small, 1-2 seconds delay and ...
2
votes
1answer
741 views
Does linux tar block write access to files
I have a large (>10GB) folder full of images on a live webserver that I need to back up and transfer.
I'm worried that if I tar the folder, the files will be blocked for reading by the webserver, ...
3
votes
1answer
467 views
Bash, fork with CLOEXEC
Can Bash execute a subprocess while preventing a subprocess from inheriting a file descriptor?
if flock -nx 9
then
# If begin program runs away, it will keep the lock.
begin program
else
echo "...
2
votes
0answers
278 views
Avoid starvation using flock with 2 process with write and read lock
I have two scripts let's call them script1 and script2.
The script1 is scheduled every 2 minutes and it takes 4 minutes to execute the script2 is scheduled every 30 minutes and it takes 4 minutes to ...
0
votes
1answer
5k views
use of lockfile in script and it significance
I have a code in which below line is used due to which i got stuck.I have hunted the web but did not understand well.just got to know the basic set of info as
below
lockfile can be used to create one ...
4
votes
2answers
2k views
Linux file hierarchy - what's the best location to store lockfiles?
I want to synchronize processes based on lock files (/ socket files). These files should only be removable by their creator user.
There are plenty of choices:
/dev/shm
/var/lock
/run/lock
/run/...
0
votes
1answer
1k views
Subversion E000037: Can't get exclusive lock on file 'db/txn-current-lock': No locks available
When I try to commit a change to a Subversion repository, and I get error messages of the form
svn: E000037: Commit failed (details follow):
svn: E000037: Can't get exclusive lock on file '/path/to/...
1
vote
1answer
43 views
Executing shell script parallelly and in background skips some operation
del_client.sh --delete client1 &
del_client.sh --delete client2 &
del_client.sh --delete client3 &
del_client.sh --delete client4 &
When I executed the commands above in the ...
-1
votes
1answer
105 views
Lock a Application Through Terminal
I was wondering if it were possible to lock a Application through Mac Terminal. I know there's a way to lock files, using chmod a+x 000 'directory', but it never worked with an Application. What I ...
0
votes
1answer
153 views
How do I check if a directory is locked or not in bash?
I have only been able to find solutions for files, and not directories, like lsof. chflags has no read option, so I don't know how to do it.
0
votes
1answer
664 views
Mandatory Locking in Unix
In Unix record locking is the technique used to lock the portion of a file for certain amount of time to maintain consistency of the
data from concurrent access to the file. On this mechanism, ...
2
votes
2answers
2k views
apt-get wait for lock release
If you are running apt-get commands on terminal and want to install stuff on the software center, the center says it waits until apt-get finishes. I wanted to know if it is possible to do the same but ...
0
votes
1answer
420 views
Accidentally deleted lock folder
I executed the following command:
sudo rm /var/lib/apt/lists/lock
due to the solution I got from here.
Now my system gets hanged more frequently while running several applications. I dont know if ...
4
votes
1answer
15k views
NFS file locking not working, am I misunderstanding?
I'm planning on having a complicated file sharing setup, and want to make sure I don't destroy file locking. (Wanting to use bind mounting, nfs, nfs over rdma (InfiniBand file sharing), and virtfs (...
1
vote
0answers
169 views
Is NFS file locking destroyed by the nfs server bind-mounting the directory being nfs shared?
I have a directory /persistent/pacmanPkgCache which is both:
nfs-shared to other machines
bind-mounted to /var/cache/pacman/pkg
Does having this directory nfs-shared and bind-mounted at the same ...
2
votes
1answer
1k views
Does linux have file locking protection when trying to rename/deleting files
I have a cron job that kicks off a new process every day. The process runs every 5 minutes and appends to a log file.
Another cron job runs every 60 minutes. It takes some of the data in the log file,...
13
votes
2answers
3k views
Is flock & exec safe in bash?
The "standard" locking snippet I've seen goes something like...
(
flock -n 200 || exit 1;
# do stuff
) 200>program.lock
Is it safe (testing seems to say so) to use exec at that point? ...
