Title: Cannot modify header warning Last modified: August 22, 2016 --- # Cannot modify header warning * Resolved [soccergrl](https://wordpress.org/support/users/soccergrl/) * (@soccergrl) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/) * I’m now suddenly getting this warning and can’t login to the admin backend anymore. Read NUMEROUS posts on this forum about this warning and simply cannot figure this thing out. I’ve checked the files for whitespace, in this case it’s complaining about my_functions.php on line 1 and pluggable.php. * My site has been working for months and I just received this warning today. The only edit I made was to the end of my_functions.php definitely not line 1. And then I tried deleting a plugin and when it asked if I wanted to delete all files and I clicked yes, this warning appeared and i couldn’t delete all the files. I then looked for the files on via FTP and none of them were there. Any help? Please! Viewing 15 replies - 1 through 15 (of 17 total) 1 [2](https://wordpress.org/support/topic/cannot-modify-header-warning-4/page/2/?output_format=md) [→](https://wordpress.org/support/topic/cannot-modify-header-warning-4/page/2/?output_format=md) * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669221) * Would you please quote the full error? * Thread Starter [soccergrl](https://wordpress.org/support/users/soccergrl/) * (@soccergrl) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669225) * Warning: Cannot modify header information – headers already sent by (output started at /home/content/p3nexnas06_data03/56/2200256/html/wp-content/themes/blankslate- child/lib/my_functions.php:1) in /home/content/p3nexnas06_data03/56/2200256/html/ wp-includes/pluggable.php on line 1178 * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669227) * You have unexpected whitespace (either a space or an entire line) on line 1 of the `/wp-content/themes/blankslate-child/lib/my_functions.php` file. See [this guide](https://codex.wordpress.org/FAQ_Troubleshooting#How_do_I_solve_the_Headers_already_sent_warning_problem.3F) for more info. * Alternatively, replacing the file with one from a fresh download may resolve the issue. * Thread Starter [soccergrl](https://wordpress.org/support/users/soccergrl/) * (@soccergrl) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669228) * No whitespace because I didn’t even touch the line 1. I did take an old file with none of today’s edits and now it works again. The only changes I made was to my login php with and action. Could this cause the problem? * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669230) * No, whatever happened was done to my_functions.php, as evidenced by it being fixed when you replaced the file. 🙂 * At some point it was modified, but it probably didn’t appear as a problem until you made the login modification. * [Pioneer Web Design](https://wordpress.org/support/users/swansonphotos/) * (@swansonphotos) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669231) * When malware on your local machine is the issue, we see responses such as: * > No whitespace because I didn’t even touch the line 1. * …and the response from above… * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669232) * Run a scan just to be sure, but don’t panic. The line could have been introduced by malware, or it could have been part of a change legitimately made at some point. Either way, you didn’t do anything to bring it about until now. 🙂 * [Pioneer Web Design](https://wordpress.org/support/users/swansonphotos/) * (@swansonphotos) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669233) * Yes, do not ‘panic’ but follow _advice_ on this related to your **local machine** and not this volunteer forum. Do you know that a local machine (computer) can compromise a site? * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669234) * What do you mean by not following advice on this forum? Seems contradictory to, ya know, offering advice on this forum. * [Pioneer Web Design](https://wordpress.org/support/users/swansonphotos/) * (@swansonphotos) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669237) * > on this related to your **local machine** and not this volunteer forum * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669239) * Ah, you mean seek malware advice on your local machine at a support system for you local machine, not the WordPress forums. * Thread Starter [soccergrl](https://wordpress.org/support/users/soccergrl/) * (@soccergrl) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669240) * These are the 2 actions I was playing with when I received the error message: add_filter(‘login_message’, ‘my_addition_to_login_form_middle’); function my_addition_to_login_form_middle(){ return ‘
[By logging in…](https://my site.com/wp-content/uploads/...pdf)
’; } * //Add Terms of Service link to login function my_login_form(){ echo ‘

*By logging in, you are agreeing to Terms of Service.

’; } add_action( ‘login_form’,‘ my_login_form’ ); * I don’t think I have any malware. * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669243) * Those lines are fine, they just probably interacted with whatever was done to my_functions.php long ago. * Nothing to worry about now. 🙂 * Thread Starter [soccergrl](https://wordpress.org/support/users/soccergrl/) * (@soccergrl) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669363) * I will try adding the code back in and see if it happens again. * Thank you for your help. * Moderator [James Huff](https://wordpress.org/support/users/macmanx/) * (@macmanx) * [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/#post-5669383) * You’re welcome! Viewing 15 replies - 1 through 15 (of 17 total) 1 [2](https://wordpress.org/support/topic/cannot-modify-header-warning-4/page/2/?output_format=md) [→](https://wordpress.org/support/topic/cannot-modify-header-warning-4/page/2/?output_format=md) The topic ‘Cannot modify header warning’ is closed to new replies. ## Tags * [cannot modify header](https://wordpress.org/support/topic-tag/cannot-modify-header/) * [warning](https://wordpress.org/support/topic-tag/warning/) * In: [Fixing WordPress](https://wordpress.org/support/forum/how-to-and-troubleshooting/) * 17 replies * 3 participants * Last reply from: [James Huff](https://wordpress.org/support/users/macmanx/) * Last activity: [11 years, 4 months ago](https://wordpress.org/support/topic/cannot-modify-header-warning-4/page/2/#post-5669386) * Status: resolved ## Topics ### Topics with no replies ### Non-support topics ### Resolved topics ### Unresolved topics ### All topics