### Context To restore the standard input, standard output and/or standard error (file descriptors 0, 1 and/or 2 respectively) of a process to the keyboard and/or display of an interactive shell (bash) session, I have seen here that one can execute either of the following: $ exec &>/dev/tty or $ exec &>$(tty) Whereas $(tty) (a command substitution) returns /dev/pts/X where X is the number associated to the currently active terminal window (pseudo-tty), thereby explicitly pointing the redirection to the "real" filename associated with the terminal in which the command is entered, in contrast /dev/tty is a character file which *seems* to appear identical to different processes (i.e. to different concurrent terminal windows). In man 4 tty it says: > The file /dev/tty [...] is a synonym for the controlling terminal of a process... In The Open Group Base Specifications Issue 8, Chapter 10 it says: > **/dev/tty** > > In each process, a synonym for the controlling terminal associated with the process group of that process, if any. It is useful for programs or shell procedures that wish to be sure of writing messages to or reading data from the terminal no matter how output has been redirected. It can also be used for applications that demand the name of a file for output, when typed output is desired and it is tiresome to find out what terminal is currently in use. ### Question Since /dev/tty is a file and not a symbolic link like /dev/fd or /proc/self, how can it "point" to different terminal processes when interpreted in different terminal windows? What does it mean in Unix/Linux parlance to be "a synonym" when not a symbolic link or a hard link — I mean: what is interpreting such a "synonym" when invoked on a command line and how?

I have set up a runit service to autologin in /dev/tty16 and the shell profile executes dbus-run-session Hyprland, however, I noticed that Hyprland, or GUIs start on the 'active' or the currently shown tty. How can I specify what tty to use a GUI application in?

OS: xUbuntu 22.04 I want to use the write / wall commands for sending msgs to other users sharing the same computer. But when I try to use the write command, I get the following error:

√ ~ $ who
user1   tty7         2024-05-12 06:40 (:0)
user2  tty8         2024-05-13 06:56 (:1)
user3    tty9         2024-05-16 06:09 (:2)
user4    tty10        2024-05-16 11:54 (:3)
√ ~ $ write user2 tty8
write: effective gid does not match group of /dev/pts/13

The error is the same no matter what variation of the command I try: write user2, write user2 /dev/pts/13 or write user2 pts/13 I have been searching online and found just a few blurbs about the error. One such blurb seemed to suggest this behaviour was intentional, at least for Debian/buntu. https://bugs.launchpad.net/ubuntu/+source/util-linux/+bug/2064685 I did try the advice in the link above to: >If you wish to restore the previous behavior, it should be sufficient to change /usr/bin/write.ul to root:tty 02755. So that now my /etc/bin/write.ul has the setgid bit set: √ ~ $ sudo chmod 02755 /usr/bin/write.ul

√ ~ $ ls /usr/bin/write.ul
-rwxr-sr-x 1 root root 23K Apr  9 10:32 /usr/bin/write.ul*

but doing so has made no change in the error received. Any ideas what more I likely need to do to get these commands working as intended?

If I open terminal and execute w command then it will show: user tty7 :0 12:04 39:56 36.87s 0.06s /sbin/upstart - Now if open terminator or xterm and execute w command then it will show it's entry in the output of w command like user tty7 :0 12:04 39:56 36.87s 0.06s /sbin/upstart - user pts/2 :0.0 12:50 1.00s 0.02s 0.00s w but it will not show a new entry when I open gnome-terminal or xfce4-terminal. Why it is showing new session for terminator and not for xfce4-terminal?

On Linux Ubuntu when at terminal I run sudo su or sudo su - the system creates a new session with a new controlling pts, namely ubuntu@ubuntu:~$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 22.04.5 LTS Release: 22.04 Codename: jammy ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ uname -a Linux ubuntu 5.15.0-124-generic #134-Ubuntu SMP Fri Sep 27 20:20:17 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ ps PID TTY TIME CMD 143254 pts/0 00:00:00 bash 143302 pts/0 00:00:00 ps ubuntu@ubuntu:~$ ubuntu@ubuntu:~$ sudo su - root@ubuntu:~# root@ubuntu:~# ps PID TTY TIME CMD 143304 pts/1 00:00:00 sudo 143305 pts/1 00:00:00 su 143306 pts/1 00:00:00 bash 143316 pts/1 00:00:00 ps root@ubuntu:~# Is it an expected behavior? As requested in the comments:

$ ps     
PID TTY          TIME CMD  
146202 pts/0    00:00:00 bash  
146231 pts/0    00:00:00 ps 

$ sudo -s 
root@ubuntu:/home/ubuntu# ps
PID TTY          TIME CMD  
146233 pts/1    00:00:00 sudo  
146234 pts/1    00:00:00 bash  
146240 pts/1    00:00:00 ps

I have several terminal windows already open; I just made a change to ~/.bashrc, and I'd like to run source ~/.bashrc in each of the open terminals. It seems to me that if I just

source ~/.bashrc | tee /dev/pts/{0..12}

, then ~/.bashrc should be run in each terminal. It looks like it was, since I include a clear at the end of ~/.bashrc. However, what I'm specifically testing is whether

PROMPT_COMMAND="history -a; history -c; history -r; ${PROMPT_COMMAND:+$PROMPT_COMMAND$'\n'}"

actually creates a single source of truth for all my terminals, and was modified in each open terminal. Now I'm not sure if this has something to do with writing to /dev/pts/{0..12} or is related to the way that history functions. If I look at one of my open terminals which is running git log, and echo $PROMPT_COMMAND, I do **NOT** see the modifications I would expect had ~/.bashrc been sourced. As a consequence of the history commands missing, I do not see git log output in a separate terminal, running tail -f ~/.bash_history, which I would expect to see if PROMPT_COMMAND was indeed modified after source ~/.bashrc. However, if I ask each terminal echo $PROMPT_COMMAND | tee /dev/pts/{0..12}, what the value of PROMPT_COMMAND is, I get:

history -a; history -c; history -r; pre_prompt_command; echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/\~}\007"

which includes history -a; history -c; history -r;, the changes that I added in ~/.bashrc. Now I'm confused. What am I doing wrong? Or what do I not understand correctly? Was PROMPT_COMMAND modified or was it not? Or is this a consequence of how bash / linux works? I'm pretty sure it's user error, and not a bug.

I am want to stream a linux terminal to my own program, and as far as I understand this is done by opening /dev/ptmx to start a new pts, I have tested this and this does indeed work (it creates a new file in /dev/pts). But I am not sure how I am supposed to actually read and write to this terminal. Writing directly to /dev/pts/(pts number) I just get an input/output error. Also, am I supposed to open /dev/ptmx and /dev/pts/(pts number) at the same time with the same program. Am I supposed to somehow open a shell first? I find this stuff kinda confusing and I have not been able to find much information except for this man page http://man7.org/linux/man-pages/man4/pts.4.html

I've been doing several chrooted environments in parallel, each in separate folder (when the script with chroot exited I sometimes run another in same folder), and for a while it seemed fine. But now I have almost empty /dev of "main" system (cannot start apps/open new windows, etc.). I've been mounting like this: sudo mount -t proc proc $work_path/fin_sq/proc sudo mount -t sysfs sys $work_path/fin_sq/sys sudo mount -t devtmpfs devtmpfs $work_path/fin_sq/dev sudo mount -t devpts devpts $work_path/fin_sq/dev/pts and unmounting after exiting chroot: umount "${work_path}"/fin_sq/dev/pts umount "${work_path}"/fin_sq/dev umount "${work_path}"/fin_sq/proc umount "${work_path}"/fin_sq/sys Occasionally I've interrupted script running in chrooted environment via ctrl-c. For cases when the script run in a folder where there were remnants of previous run, the script is coded to umount and delete previous work. Today I saw target is busy at least in one terminal window where I run script with chroot. After umount failed the script deleted all folders of chrooted system. For the future, I think I better cancel further unmounts/deletions if one of umounts fails. However, what do you think might cause such result? How to investigate? How to get system to working condition? I'm not rebooting the system for a while hoping to learn Linux deeper. TIA P.S. full script(s) for those interested: script running other script via chroot , searching for /dev/pts finds two lines (mount/umount) in the code. "Naturally" lsof shows empty output and adding --force seems to make no difference. Trying mount -t devpts devpts /dev resulted in "devtmpfs already mounted on one_of_chrooted_paths/dev". I've read https://unix.stackexchange.com/questions/464585/umount-target-is-busy , but the question is for -o rbind, I mount w/out it. Again, it was working with two chrooted, I increased to 3-4 and something broke...

This is still related to my [yesterday thread](https://unix.stackexchange.com/questions/703218/annoying-clocksource-alert-warning-in-bash-prompt-periodically) , so there's alert or maybe it's just log that displayed on my terminal on

/dev/tty1

. Ofcourse it's annoying because it's displayed in my bash prompt, so whenever I want input something, my input has been overwrite with that output. It came printed out periodically maybe about

second

. So you can see how it's annoying My terminal is moreless looks like this:

root@LFS:# echo "Hey get out of there"clocksource: timekeeping watchdog on CPU0: acpi_pm wd-wd readback delay of 643744ns
clocksource: wd-tsc-wd read-back delay of 182144ns, clock-skew test skipped!
clocksource: timekeeping watchdog on CPU0: acpi_pm wd-wd readback delay of 643744ns
clocksource: wd-tsc-wd read-back delay of 182144ns, clock-skew test skipped!
clocksource: timekeeping watchdog on CPU0: acpi_pm wd-wd readback delay of 643744ns
clocksource: wd-tsc-wd read-back delay of 182144ns, clock-skew test skipped!
...

I suspect this is not because of

, but

output. Because when I command

. It display same. But whenever I use

/dev/pts

There's no annoying output or alert that came periodically, I tested it when I login SSH in my LFS sistem. So how to prevent dmesg log displayed to

/dev/tty1

Update: Inside

/proc/cmdline

root@LFS:~# cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-5.16.9-lfs-11.1 root=/dev/sda1 ro

So I have the following situation: I have a host that exhibits unexpected behavior when using ssh -t combined with tmux. If I call ssh -t my-problem-host tmux non-ascii characters (e.g. €) are displayed as _. If I connect without calling tmux, there is no problem. For example ssh -t my-problem-host bash followed by manually entering tmux is OK, while ssh -t my-problem-host bash tmux is not OK. Other strange behavior outside of tmux: If I use ssh -t my-problem-host vim and enter a special character, I get the special character and a space. If I use ssh -t my-problem-host mc and type a special character, I get two questions ??. I also have this problem only with a single host and would like to know what causes this and how this can be fixed. Essentially ssh -t seems to cause problems, the host seems to have a strange pseudo-terminal.

How can I change pts/1 to another value? Can I add a user with adduser and give a own parameter to change this?

Hey guys I tried to activate multiuser for some screens so I used screen -A -m -d -S test screen -S stest -X multiuser on screen -S test -X acladd testuser But I got chmod /dev/pts/17: Permission denied Unfortunately I thought it would be a great idea to play around with the permissions. Now I´m with the folder it self drwxrw-rw- 2 root sys 0 Jul 10 09:39 pts And the files inside with the following total 0 crw-rw-rw- 1 root sys 136, 0 Aug 4 22:30 0 crw-rw-rw- 1 markus mTeam 136, 1 Aug 1 23:20 1 crw-rw-rw- 1 markus mTeam 136, 10 Jul 24 13:47 10 crw-rw-rw- 1 markus mTeam 136, 11 Jul 27 17:43 11 crw-rw-rw- 1 markus mTeam 136, 12 Aug 4 22:33 12 crw-rw-rw- 1 markus mTeam 136, 13 Aug 4 22:32 13 crw-rw-rw- 1 markus mTeam 136, 14 Aug 4 22:33 14 crw-rw-rw- 1 markus mTeam 136, 15 Jul 27 20:12 15 crw-rw-rw- 1 markus mTeam 136, 16 Aug 4 21:46 16 crwxrwxrwx 1 markus mTeam 136, 17 Aug 4 2021 17 crw-rw-rw- 1 markus mTeam 136, 18 Aug 4 22:07 18 crw-rw-rw- 1 markus mTeam 136, 19 Aug 4 16:29 19 crw-rw-rw- 1 markus mTeam 136, 2 Jul 27 17:43 2 crw-rw-rw- 1 markus mTeam 136, 20 Jul 27 17:37 20 crw-rw-rw- 1 markus mTeam 136, 22 Jul 27 17:43 22 crw-rw-rw- 1 markus mTeam 136, 23 Aug 1 20:16 23 crw-rw-rw- 1 markus mTeam 136, 24 Aug 4 17:55 24 crw-rw-rw- 1 markus mTeam 136, 25 Jul 27 17:43 25 crw-rw-rw- 1 markus mTeam 136, 28 Jul 27 12:29 28 crw-rw-rw- 1 markus mTeam 136, 29 Jul 27 17:43 29 crw-rw-rw- 1 markus mTeam 136, 3 Aug 4 22:24 3 crw-rw-rw- 1 markus mTeam 136, 31 Jul 27 17:43 31 crw-rw-rw- 1 markus mTeam 136, 33 Jul 27 17:43 33 crw-rw-rw- 1 markus mTeam 136, 4 Aug 4 22:33 4 crw-rw-rw- 1 markus mTeam 136, 5 Jul 13 10:01 5 crw-rw-rw- 1 markus mTeam 136, 6 Aug 4 22:14 6 crw-rw-rw- 1 markus mTeam 136, 7 Aug 4 22:14 7 crw-rw-rw- 1 markus mTeam 136, 8 Aug 4 22:33 8 crw-rw-rw- 1 markus mTeam 136, 9 Jul 10 09:41 9 crw-rw-rw- 1 root sys 5, 2 Jul 10 09:39 ptmx On some other pages I have read that the permissions can change and aren't static. And my problem is now that since I changed the permissions I'm not able to create new screens nor operate them. When I use for example: screen -A -m -S test I get Cannot open /dev/pts/27: Permission denied So is there a way to fix my stupid mistake? I'm grateful for every help I get :) I'm using Ubuntu 20.10

I read that pts is a pseudo-terminal (that we get through ssh or xterm) and tty is the native terminal. I didn't connect to my PC through ssh or xterm, but I am still getting pts/0 and pts/1 when I type who command. When I open other terminals, the number of pts's increase.

username@machine$ who
username tty7         2020-12-30 11:39 (:0)
username pts/0        2020-12-30 11:39 (:0)
username pts/1        2020-12-30 11:53 (:0)

I am not getting why this is happening, shouldn't there be more tty's after opening other terminals? Also, when I do su I see that other pts session gets opened for root in auth.log file.

A virtual machine (using linux+kvm+qemu) is setup to provided a serial port for a terminal, which is made available via a pseudo-terminal, some random /dev/pts/ I use screen as a way to interact with /dev/pts/, as it has proven better than cat /dev/pts/ & cat > /dev/pts/ which did not correctly handle escapes like ctrl-c, or echoed input multiple times. The issue and core of this question is that the settings of the "tty/pts" as inquired via stty --all inside the shell wihtin screen /dev/pts/ does not have the correct settings with respect to the dimensinos (cols and rows) which effectively causes headache by incorrect line-wrapping etc inside the shell of the VM. Since there is more than 1 machine and terminal/tty/pts at play here I am not experienced enought to understand how to setup the correct settings. How can the screen /dev/pts/ shell be made aware of the correct stty settings? ** Update ** The output of stty --all within the shell of the vm is. root@mail:~# stty --all speed 115200 baud; rows 24; columns 80; line = 0; intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = ; eol2 = ; swtch = ; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0; -parenb -parodd -cmspar cs8 hupcl -cstopb cread clocal -crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon ixoff -iuclc -ixany imaxbel iutf8 opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon -iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc the output of stty --all in the shell of the hosting system is speed 38400 baud; rows 39; columns 147; line = 0; intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = ; eol2 = ; swtch = ; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0; -parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl -ixon -ixoff -iuclc -ixany -imaxbel iutf8 opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc

A pseudoterminal has a pair of master and slave. How can we find out the master device file from a slave device file (e.g. /etc/pts/3)? I only find /dev/ptmx and /dev/pts/ptmx, but they can't be shared by multiple slaves. Given one of the processes working on the master and slave, how can we find out the other? For example, ps provides information about the controlling tty of each process. Can it be helpful? Thanks.

i was wondering if it is possible to force log out a user (anyone other than root) when trying to login via tty (ctrl+tab+f1/f2/f3..). The user should be able to use pts with no problems. Using CentOS 7.

I've written a shell script that uses the trap feature to output its progress when it receives a SIGUSR1 signal, but I don't see how to have the script be able to output the progress to the STDOUT of the process which sent the signal. So, if the script is running in terminal emulator /dev/pts/10 and I send the process a signal from a terminal emulator on /dev/pts/11, the output is going to /dev/pts/10, but I want to send to /dev/pts/11. I do NOT want to have to resort sending the progress message via wall or hard-coded shell redirection to a specific STDOUT.

I'm trying to figure out how I can reliably loop a read on a pt master I have. I open the ptmx, grant and unlock it as per usual: * ptmx stuff */ /* get the master (ptmx) */ int32_t masterfd = open("/dev/ptmx", O_RDWR | O_NOCTTY); if(masterfd ptmx = masterfd; Next I save the slave's name (yes I know sizeof(char) is always 1) /* get the path to the slave */ char * slavepathPtr; char * slavePath; size_t slavepathLen; if((slavepathPtr = ptsname(masterfd)) == NULL){ perror("ptsname"); exit(EXIT_FAILURE); }else{ slavepathLen = strlen(slavepathPtr); slavePath = (char *) malloc(sizeof(char) * (slavepathLen + 1)); strcpy(slavePath, slavepathPtr); }; I then create a predictably named symlink to the slave (/dev/pts/number) in /dev/custom/predictable (which was provided as an argument to this program using getopts) and verify that its permissions are safe using calls to access, lstat, readlink, symlink and confirm that the program can continue execution, otherwise it calls unlink on the symlink and terminates the thread. Finally the program ends up in this loop ssize_t read_result; ssize_t write_result; while(1){ if((read_result = read(comms_in->ptmx, ptmxio_read_buffer, sizeof ptmxio_read_buffer)) thread_statuses[PTMXIO_THREAD] = THREAD_FAILED; pthread_mutex_unlock(&COMMS_MUTEX); pthread_cond_signal(&SIG_PROGRAM_FINISHED); pthread_exit((void *) comms_in); } }else if((write_result = write(STDOUT_FILENO, ptmxio_read_buffer, read_result)) != read_result){ { /** same as above */ } }; }; On the system, I can run this program and all is swell. The read blocks. When the pts symlink is opened with cu or picocom then bytes are successfully read up to the buffer limits either on my end or the kernel's end, depending on who's lower. The problem comes when the slave is closed. At this point, the read returns -1 -> EIO with error text: Input/output error and will continue to do so, consuming a lot of cpu time if I choose to not terminate the thread and loop. When cu or picocom or even just an echo -en "some text" > /dev/pts/number, the read blocks again, until bytes are available. In the case of the redirection into the symlink, obviously if it fills less than a buffer, read just gets that one buffer and continues to return -1 -> EIO again. What's going on? I need a method that doesn't consume a lot of CPU as this runs on a slow embedded application processor and allows me to re-establish reads without losing bytes. I noticed a thread making a call to this: ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) and can't make much sense of what the 3 options are as they're not in my Linux headers anywhere.. Note that 3 is comms_in->ptmx / masterfd. Here is an lstat on the symlink and some extra information, note that the st_mode is unchanged before and after successful and unsuccessful reads. ‘ptmxio_thread’ failed read (-1) on /dev/pts/13 /dev/pts/13: Input/output error ‘ptmxio_thread’ ptsNum (from ioctl) 13 ‘ptmxio_thread’ st_dev: 6, st_ino: 451, st_mode: 0000A1FF, st_nlink: 1 ‘ptmxio_thread’ st_uid: 000003E8, st_gid: 000003E8, st_rdev: 0, st_size: 11 ‘ptmxio_thread’ st_blksize: 4096, st_blocks: 0, st_atime: 1540963806, st_mtime: 1540963798 ‘ptmxio_thread’ st_ctime: 1540963798

There seem to be plenty of similar questions, for example: https://stackoverflow.com/questions/5374255/how-to-write-data-to-existing-processs-stdin-from-external-process However the answer given is to prepare the program beforehand by making its stdin a pipe. There's also: https://serverfault.com/questions/178457/can-i-send-some-text-to-the-stdin-of-an-active-process-running-in-a-screen-sessi Which is answered by commanding a terminal multiplexer under which the program in question is running. That means it also needs prior preparation. This question is about how to do this *without* having done any preparation beforehand. At first I thought it might be as simple as:

echo foo > /proc/$p/fd/0

but that just writes to the terminal. So then I tried:

echo foo > /proc/$terminal_emulator/fd/$ptmx_fd

but that also fails because it just opens up a new terminal device slave for echo. I already have an answer using gdb (*sigh*) which I'll be posting below, but I wonder if anyone knows of a simpler and better alternative.

I am trying to find out which tty or pts is being run by which process. My research so far is that: - tty is a kernel or backend terminal to handle lower level stuffs - pts is a pesudo terminal to allow user to communicate with the system - there are a lot of tty and pts files in /dev but cannot be read Would like to ask the following questions: - Why does /dev/pts and /dev contains so much numbers (eg 1-26) despite ps -aux | grep pts only showing 4 pts entries - Is it possible to determine what process is running a pts or tty? As I read that ssh spawns a new shell, but not sure if its a pts or tty