What ! Is it true?

Yes it is true, I have visited it in Kashan.

'Omar according to the Encyclopedias
According to the Sunnis, 'Omar Ibn Khattab Ibn Nofail-e Gharashi, born 40 years before the lunar calendar (i.e. 40 before the age of Islam), was the second Caliph, or the second successor to prophet Muhammad. 'Omar played a crucial role in the expansion of Islam: what are now known as Algeria, Egypt, Iraq, Syria and Jerusalem were all conquered during his ten-year rule as Caliph. He was the first to earn the religious title of Amir al Mo'meni (here, too, Shi'i Muslims beg to differ). 'Omar is regarded as one of the most enlightened and courageous religious figures.
'Omar was actually related to 'Ali and his wife Fatemeh, since he married their daughter 'Om-e Kulsum. His own daughter Hafse was married to the prophet Muhammad.
'Omar was killed by a slave by the name of Abu Lo'lo', in the month of either Muharram or Zihaje, during the year 24 according to the lunar calendar, and was buried next to the prophet himself.

The Occasion of 'Eid-e 'Omar according to Women's Oral History
'Eid-e 'Omar is celebrated between the 8th and the 18th of Rabi' al avval, the prophet Muhammad's birthday. According to this Iranian tradition, 'Omar was killed precisely on the 9th of Rabi' al avval. The event is also known by the caustic name of 'Omar-koshun ("the killing of 'Omar"), yet what is striking is that the participants still largely agree on 'Omar being "one of the greatest men of his time". 'Omar's importance, and his supposedly outstanding qualities, are not at stake here.
On the other hand, he is said to have deeply begrudged Fatemeh and 'Ali, for their close relationship to the prophet, and for being so popular and honored. Among the stories the women tell every year during 'Eid-e 'Omar, one is about the bagh-e fadak, the Fadak garden, which Muhammad's family would cultivate, and the produce of which was distributed among the poor. Some say the Fadak garden was actually part of Fatemeh's dowry, and that, as the story goes, one day, as 'Omar sees Fatemeh coming from the garden, he demands to see her land documents. When she shows them to him, he snatches them and runs off.
Another story concerns the time when 'Ali is brought to the mosque, and 'Omar's supporters try to force him to swear allegiance to their mentor. When Fatemeh hears this is going on, she runs over to the mosque, and holds a long and fiery speech. "If you don't leave him alone", she tells them, "I'll curse you and pray for your deaths". The plan works, and they let her husband go.
Ghonfos (or Ghonfoz), a figure that exists only in oral history, was one of 'Omar's followers. He comes looking for 'Ali one day, to take him to see 'Omar once again, but Fatemeh comes to the door, and tells Ghonfos her husband had gone out. So he leaves, and, shortly after, it's 'Omar himself who shows up, demanding to speak to 'Ali. Once again, Fatemeh, speaking from behind the door, tells the visitor that 'Ali isn't home. But 'Omar kicks the door open, injuring Fatemeh at the hip, and slaps her in the face. Fatemeh had been pregnant at the time, and because of the blow from the door, she loses her child.

The Ceremony
From the first of Rabi' al avval, immediately after Muharram, the month of religious mourning, the women start sewing clothes of all colors, particularly red. Some dye their hair and nails with henna, others make for the hairdresser, and when the ceremony finally begins, everyone is dressed up in a bright and colorful way.
At the ceremony, which takes place at people's homes - women and men are invited to separate gatherings - the women sing, dance, and recite lewd poetry ("ya Zahra, ya Zahra * Zahra is another name for Fatemeh*, congratulations, your husband's enemy has gone off to hell, etc."). Tambourines, pots and pans are used to beat the rhythm. A small, colorful doll is prepared for the occasion, representing 'Omar, which is placed in the middle of the room for the women to dance around, and which is burned at the end of the ceremony.
The ceremony doesn't only concern 'Omar, but Fatemeh as well, and the difficulties she faced. 'Eid-e 'Omar actually serves as an occasion for women to share their troubles, to discuss women's problems in general, and those of wives and mothers-in-law in particular. Women who are going through a hard time, and those who are about to marry, come to the ceremony dressed in carnevalesque outfits, with elaborate makeup and circus-like clothes.
Some women dress up as men, wearing false beards and moustaches, suits and ties, and choose a woman to dance with. At one point, a rival woman shows up to attract the man's attention, and seduce him into dancing with her instead. Traditionally, in these mock seduction scenes that are played out during 'Eid-e 'Omar, the newcomer has her way.
Until the revolution of '79, the men would celebrate 'Eid-e 'Omar in public. Today, children still play around with 'Omar dolls and burn them in the streets. Yet the government has never been keen on a celebration so offensive to Sunni cultures being carried out in full view. Nowadays, a representative of the government is sent to all the get-togethers, to make sure the occasion doesn't get all too festive and malicious; more recently, for example, the officials have been discouraging people from dancing, suggesting they just clap instead.
Styles and tastes have changed, too. One group of women told me about a blind man with a beautiful voice that they would invite to their 'Eid-e 'Omar ceremonies to sing for them � since he was blind, they could dress and dance any way they pleased in front of him, without breaking any rules. Nowadays, this would be considered very poor taste, and anything but a woman singer is unlikely.
If what I've described so far is typical for "popular" or "lower class" ceremonies, it's important to note that 'Eid-e 'Omar is also celebrated in wealthy families (the middle classes appear to be less interested). Among the wealthy, however, the festivities look very different, with everything from the food to the dress to the music being more refined. On one occasion, I saw a video monitor being set up by the main room so the rest of the crowd could watch from outside.